WF,
You want mountains and bush - come to BC! Best times are probably late Aug early Sept...north of the city is bush / mountain paradise, with the Cascades and Coast mountains rising up to the 10,000ft (+!) mark...its full on mountain flying tho (not trying to belittle the welsh mountains of course!) and any club you rent from will almost definitely insist on a mountain check of about 2 hrs (a very good idea!) This is fun though, and if you are lucky you might even get to do a bush landing (search for "tipella" as a BC airport! - 2500ft of dirt carved out of a forest surrounded by mountain walls!)
I suggest you think about places to rent around Vancouver - Boundary Bay airport is perfect for this -
www.czbb.com
Check out the place I train at - which has good a/c availability
www.pacificflying.com
Cheers, Finals!