I love a fellow chilli grower. I live in Scotland, which probably had the same issues you have with regards to light/climate etc. It's an obvious question so forgive me but when you mentioned small yields I wondered if you fertilised regularly? I had experienced small yields with my chillis. My favourites to grow are jalapeños and scotch bonnets. I read online about fertilising weekly and upgrading the strength of the fertiliser when the plants were flowering/fruiting. This made a colossal difference to my yields.

Anyway loved your post!