Hey Dave,
You actually got lucky and stumbled across the right one here..most harness are designed to be somewhat comfortable for long durations, and big wall climbing definitely more than say..sport (usually you're not hanging as long) but it sounds like for what you are looking to do, this is a good fit.

Dave,

This is what you want.

http://www.backcountry.com/outdoorgear/Black-Diamond-Bosuns-Chair/BLD0965M.html

Don't get this harness. Your legs will still go numb after a while. The goal is to get the weight off your harness. Any cheap harness and this chair will do the trick.