This may not be very helpful but personally I don't like ranges aimed specifically at plus sized people - don't find the quality of Evans, Simply Be etc good enough. Ditto supermarket stuff.
Much of my stuff is carefully chosen Boden, who go up to 22. I'm prepared to do a lot of planning, ordering, and sending back to find the right dresses and tops, etc from there each season.
All my jeans are NYDJ, which I recommend.
Monsoon of course also go up to 22, though I'm not a huge fan of their stuff - just not my style.
I used to buy quite a few basics from the M and S Autograph Weekend range but this sadly seems to have vanished and Autograph generally gone downhill, so seldom buy anything there. But you can still sometimes find the odd OK basic in one of the big M and S stores.
When I worked in an office most of my clothes came from Marina Rinaldi, Maxmara's plus size label (the only specialist one I really buy from). But it is £££ and does need careful choosing, like any other label.