Nostr.wine is a good one. It's a paid relay that connects to other relays for you to blast your notes far and wide. You'll be able to discover a lot of others since it connects them to you even if you're not specifically on their relays.

I wish I knew more about relays to make a good suggestion, but when my feed is slow I literally do searches for various hashtags and always end up finding interesting people or conversations. I will check out Nostr.wine based on the first reply to your post.