Thanks for the detailed response!
There are neutral lines at the switch iirc, but may not be for all the circuits (two were added at a later date), I will have to check. The biggest problem I face is getting a smart switch to fit the double size!
I wanted to avoid another hub for her, as more hubs means more points of failure. As I have to manage her smart home for her, it’s whatever makes my life easier in the long run!
On the subject of the micros, is there a preferred brand between Fibaro and Aeotec? I guess they are both natively supported in ST. Will they update firmware through ST if required?
Looking on Amazon, seems little difference in price between them.
I’m already planning to change the switch, so that’s not a problem. Would a standard on off not suffice? I’ve seen various wiring diagrams of different setups, although the momentary switches do seem to be the way to go…
The box is the standard depth, not the deep one. I guess it’s possible to change, as it’s in plasterboard wall.
That’s sounds like what I’ll have to do.
Would these be suitable?
https://www.screwfix.com/p/varilight-z2dg102srs-10a-2-way-off-retractive-switch-brushed-steel/38220
After looking at the MK ones, I think they may be too hard to press for my mum.
Great, I’ll see where I can get one of those from.
Thanks for your help 
Hi,
You could try putting 3no retractive switches in a 2g frame (plenty of manufacturers) and then add a dimmer module at each light you’re controlling.
The added advantage of that is you will have a neutral at the light but rarely have them at the switch.
Try these, there sold as being able to be put onto other dimmer plates. No neutrals needed, I’ve just fitted a single and was easiest switch I’ve ever done
Was going to mention these too 
. Not that I like rotary 
but you can literally replace your old modules with these and continue using them.
So for push to make of centre off switches in the UK check out click and there mini grid range. I use the Deco range but there is loads of options and at a great price point. Your need to get from a wholesaler though.
These are fully ST compatible?
Yea, just paired as zigbee dimmer
https://www.cwberry.com/Electrical-Supplies/Light-Bulbs/LED-Light-Bulbs/LED-GLS-Lamps/Aurora-AU-A1ZB2WDM1P-250w-Smart-Rotary-Dimmer-on-1-Gang-Plate_07102487.htm
Then these would be a far simpler option than fibaro micro dimmers. Think I’ll cancel the order and get these instead. Means I don’t have to change the back box and cuts down on wiring!
@rickydg
Just to bring everything together.
The only smart 3-gang smart light switches/dimmers I have seen in the UK are the LightwaveRF and TheDen. Both require their own hubs and currently TheDen is not integrate-able with any other systems including Smartthings. TheDen do either a 3-gang switch or a 1 or 2-gang dimmer. LightWaveRF do a 3-gang dimmer.
The next common option is to use micro modules like Fibaro, Aeotec, Insteon. Fibaro and Aeotec are Z-Wave and could be used directly with Smartthings but Insteon requires an Insteon hub. These are all available in either switch or dimmer versions and one of the big advantages of these is that you would mix dimmers and switches in the same 3 or 4-gang faceplate. These all would also require using momentary switches like the ones mentioned by @anon36505037
The final option is Aurora AOne as mentioned by @mark_cockcroft this fits on the back of many standard dimmer faceplates but possibly not all of them. This can either be connected directly to Smartthings or has its own hub.
https://aone.auroralighting.com/ProductDetails//AU-A1ZB2WDM
Note: AOne does not have a switch i.e. on/off option only a dimmer option so might not be suitable for all lights.
I am currently leaning towards using Insteon micro modules myself. Insteon have recently announced they intend to launch a new hub with multiplatform support including Alexa and HomeKit. It is also possible to use momentary pullcord switches for use in bathrooms with micro modules including Insteon. Another bonus of Insteon is that they also do plugin switches and dimmers for table lamps.
Nice Summary!
On this:
Insteon doesn’t have an Integration with SmartThings other than IFTTT, though, right? (HomeKit is not a new integration for them if you have the right model hub, although they’ve been talking about doing a lot of new stuff now that they have a new CEO.)
@JDRoberts
There was this
I don’t know if it still works.
Of the two types of Insteon hub, the Pro which supported HomeKit has been discontinued for some time and only supported HomeKit and nothing else. The normal hub which could in theory be used with the above app to link to Smartthings also officially supports Alexa and Google Assistant but not HomeKit.
The supposedly brand new hub referred to in the Insteon blog will support Alexa, Google Assistant and HomeKit/Siri and supposedly be more open to others like Smartthings. In otherwords ‘one hub to rule them all’. 
I have friends who have one. It definitely supports both HomeKit and most of the regular Insteon devices. ( they had a big insteon set up before switching to that hub to get HomeKit integration.) I don’t know if it ever worked with echo, they don’t have one. I’ll ask them about IFTTT, but my guess is they don’t have that set up either.
@JDRoberts
Yes the Pro hub supports the same range of Insteon devices the issue is that it is not controllable by Alexa and Google Assistant nor other options e.g. Smartthings only via HomeKit and the special Pro version of the Insteon app.
The new hub will also have a new app which is already in beta.
think we have gone off topic, was looking for not haveing an extra hub. ie z-wave or zigbee (or wifi with sutable middle man)
Are the Fibaro micro modules better than Aeotec?
Thanks
Simple answer yes!
I have a fibraro dimmer 2 module and I have a lot of bother with it!