My post here could be relevant.
After trying many I recommend any good quality pannier rack backpack. My favorite is OAK25 (I can not guarantee quality):
https://www.amazon.de/OAK25-Pannier-Rack-Women-Black/dp/B0CLV2XP7T?ref_=ast_sto_dp&th=1&psc=1
pros
look elegant
does not add much width
very lightweight… only 700gm!!
cons
hard to fit wide stuff in