I was in the same boat as you (only owing BPs and boas) I purchased a jaguar carpet python a few months ago and they are much more active when out than either boas / BPs. They are also harder to tame, verses my boas that have never struck at me, this little guy has gotten me maybe 6 times since purchase and is much faster than the Boas.

I would say a carpet would be a good choice... Some get as large or larger than a boa, just not as heavy, and it is a step up in terms of activity and feistyness from a boa, but not as much as a retic. Plus, SD retics are very pricey right now (if you want a morph) and dwarfs can still get 12'... So unless you want to jump to something that big and / or expensive, I'd say go for a carpet first. I know I'm enjoying mine and he is gorgeous.