Is your current pool a liner pool? Do you have any ground water issues right now?
I ask because I'm in Pittsburgh as well with a liner pool and we've had it float a few times. If you've had this it's worth installing a sump pump in the yard by the pool to catch groundwater.
A stand-alone spa is a good choice. Ours is next to our pool and right outside our back door. I use it year round, and with a heavy duty cover we've never had an issue keeping it warm.