Well I don't think there are any Trader Joes in the UK but everything else I'm sure you can find in local stores or online.
As far as styles, I suppose you can wear your hair in box braids or similar styles that you can get done at a braiding shop.
If I were you, I would practice doing styles on your own because there may be few salons that will cater to natural hair once you become fully natural. I'm no style guru. I just stick to braid outs and twist outs primarily. Those just entail putting any number of braids on each side of your head after shampooing and then letting them dry. Take them out, fluff and go! lol.
YouTube and natural hair blogs will be your best friend while transitioning. I learned so many tips that really helped me along the way. There will be a lot of trial and error and sometimes your hair will not turn out like you want it but that's ok. You just have to be willing to practice and be patient with your hair.