UK down-lights (recessed) recommendation for an extension

The only problem with smart bulbs is if you wish to control them with ST, you have to leave them switched on. If you turn the light switch off no more control.
Personally I would go with either a smart light switch to control the lights or maybe a Fibaro dimmer. This way you can still control the lights with ST and also manually using a standard light switch.
There is a topic already on this.
Search for FAQ. Lighting options for the UK.