Am I correct in assuming that you are in the UK?
If so, the easiest thing is just to get a socket adapter and then use an E27 RGBW lamp.
This is a typical converter, but there are many available.
Osram makes an E 14 for their lightify series which is on the official SmartThings compatibility list, but it’s a tunable white, not RGBW.
See the existing discussion thread (this is a clickable link)
And here’s the Osram bulb, but again, that’s white only.
https://www.amazon.co.uk/OSRAM-Lightify-Smart-Connected-Light/dp/B00YSXBHS4