I would also say go with a BCI or a Dumeril's boa based on what you described.
I love my dumeril's to death but she was a pain in the tail end to get eating until I caved and got her something live. I've been trying to convert her (i.e. 2 hrs ago) but she just flat out isn't interested in f/t, and from what I've read that can be typical of young ones but they tend to be garbage disposals once they grow up. Plus the fat adult female dumeril's the friend I get my live feeders from has that my gf was talking about is about the biggest sweetheart a snake can be, and even my young one isn't the slightest bit nippy even when she's stressed.
I also have a baby BCC female that is totally calm and handleable, but keep in mind that not all snakes are alike. And as a generality young boas can be defensive and nippy but they can also quickly grow out of it. And a big difference between a BCC and a BCI is size, unless you're talking about a male a BCC will typically be larger than an BCI. Males can go either way really.
Bottom line, based on what you said a boa would be the way to go, just make sure you practice proper quarantine procedure to protect your established BP.