Hey guys, I'm more of an electric bassist, not having played the double bass extensively for about 8 years now, but now I've picked up the double bass again, this time in more of a jazz mindset rather than orchestral like I did in high school. However I've noticed that usually about halfway through a DB gig, my picking hand thumb starts to get pretty sore from resting it on the side of the fingerboard (actually, more on the corner nearest the top of the body). My question is, would this be a situation in which I just need to build up a callus, or should I maybe have that corner of the fingerboard rounded to less of an edge? I've also thought about getting one of those rubber thumb caps that the postal workers use to sort though papers, odd as that sounds. Any other suggestions?