Shops I frequent:
Ice crystal shop
You do you though. Dip your toes in a lot of different shops, find out what you like. There are a lot that I didn't mention that are also viable (spooky foods, royal potionery, collectible cards, etc.)
Just be wary of HTS items. It's nice to have some shops where you make a bunch of profit with buyables that you can throw in your shop to get consistent low-effort cash alongside the shops where you can potentially get high profile, high rarity items.