Two perspectives

I haven't run across many books that alternate between first and third person, but that doesn't mean there aren't a number out there or that it can't work if done well.

I've read quite a few multiple first-person pov novels that worked, in my opinion. The Poisonwood Bible by Barbara Kingsolver on the more literary end of things, and Havemercy by Jones and Bennet on the more genre fiction end (it's a fantasy novel). I don't read much genre romance these days, and the ones I remember were all third person omni or limited third, with more time spent with the female protagonist, but those were a long time ago.

I have a bit of a thing for doubling perspectives, so I'm glad to hear you're considering it! I think they can be very effective depending on why you as the author want to write it that way. I had storylines in different times that eventually overlapped and dedicated alternating chapters to the two main protagonists. I used third person rather than first person perspective, but I've definitely read books that use first person and it wasn't intrusive. I think you need to decide third or first but stick to that for both characters, otherwise that could get awkward for the reader.

Hope that helps!