I honestly don't care for STV. I mean, I'm glad to hear you're interested in a change. To me, STV adds a new level of complexity that isn't necessary. If you're going to continue with single riding representation.
Otherwise, STV simply IS IRV/AV.
Edit: I should note that in the UK, it might be logical to go to an STV system, but that would involve a lot of larger reforms - the removal of ridings, for instance, that won't have these sorts of difficulties with AV. AV is a more fair system, and it's a good leaping point to STV for the next generation.
I also have a difficulty with the "extra votes" thought of STV. Who determines what votes are extra is the question I don't care for...and I think that if you're going to have a STV-style vote, you might as well go right to PR.
In Canada, I support reforming the Senate to be a straight PR-based system, while using IRV in the local ridings.