Print Sisters - beautiful prints (doh!) and textiles. Currently got two prints to frame and hang and got my eye on a couple of cushions.
Etsy - I've bought frames, door knobs and handles, cupboard lining paper from there recently.
SCP/Skandium for when I'm feeling more flush (not recently).
Holloways of Ludlow/Heals for lighting.
If money were no object, Skinflint for reclaimed lighting. Fabulous pieces, but will just have to look., barring lottery win. But if £400 for a mid-century pendant from Soviet-era Czechoslovakia is in your ballpark, you won't find better.
Heals for bed linen. I wait for the sales.
Royal Design for lots of Scandi brands in textiles and ceramics.
Mad About the House is a design blog I enjoy and she (Kate Watson-Smythe) does a design store edit of fundamentals for each room and accessories.