i'm quite interested in old seeds, heritage seeds that have sown good performace in different conditions.
many commercially sold seeds are optimised for high yield in targeted conditions, not hardiness nor less usual conditions.
also: buy open pollinated if you can, so you can save seed (many bought seeds are F1 hybrids, their offspring are infertile.
local seed swap meet ups are a great thing
to buy, reel seeds in Wales are a lovely bunch:
https://realseeds.co.uk