Im a big fan of the inflatable pads. Got a nemo and a thermarest. Both seem to do the job.
@EYJONAS! have looked at the exped pads and the one I was looking at was really thick like you mentioned and really comfortable, just didnt seem to pack down very small.
I would encourage you to go with a stock design that you like. Lots of good options out there that will fit the bill if not wanting a chasis stock. That's the best part about building a rifle, you can pick what components you want. I would think as long at it is one of the quality stocks out...
Only accurate rifles are interesting- Townsend Whelen
That being said if it looks good and doesn't perform, its gotta go down the road or the smith to get fixed up.