How much larger should Jockey shorts be than normal?

I think the title about covers my question.  I'm starting to assemble items we'll be needing and that is something I'm confused about.  I mean if I buy them to big they won't hold the pad in place and if not big enough the waist band will hurt his incisions.

Oh great Glen.  That relieves my mind on what size to get for him.   Thanks!!

he can wear his normal underwear, but should try the undergarments, too. he won't need them, though, until the catheter is removed. Jeff did not wear any underwear while he had the catheter in. he just wore very loose soft cotton large shorts. he came home from the hospital with the shorts and a baggy T-shirt.