Like you Henry, +1 for tight boxers.
First few weeks for me, post op, there was significant scrotal swelling and discomfort. Coupled with the limited recovery of continence requiring a big pad, and the first few days after catheter removal required 'baggy but supportive'- OTT support squashed things uncomfortably. Once things stabilised and continence improved to allow a Level 1 pad, I found that wearing a jockstrap type brief gave good support, but not without a downside: The op seems to have left me with persistently more painful epididymal cysts on the L testis, and so maybe I require more supportive underwear than some- The side of the jockstrap sometimes ( not always) digs in to the groin on the Left, where the vas deferens to the testis is.
Wearing a pad reduces the ventilation of the saddle /genital region compared with pre op. A consequence of this is that the balls, being hotter inside a pad, drop lower, and the muscular sling in the scrotum relaxes and thus has to be assisted with supportive pants to prevent worsening ache. So, looking for something that was breathable and supportive, I found that the X Bionic 'Energizer' ,boxers I have used for years when engaged in sweaty outdoors activity, did the trick. Not cheap at about £25, and you'll need them on the smaller side, but good support and comfort. They are tight boxers, so even though 'wicking' and very breathable, they can feel a bit warm in hot weather, and light duty pads seem to shift out of position a bit in them if active. Jockstrap briefs seem better for keeping things in place.
A problem I found with choice of jockstrap was that the purposefully supportive 'sportswear' ones were rather warm and bulky, whereas the more fashionable ones appeared to be minimally supportive. I realised i couldn't take myself too seriously when I ordered some which had the logo PUMP! emblazoned across the waistband. My excuse for buying them is that they do the job, can fit a level 1 or 2 pad, and as they're ice blue in colour they're not too lurid!
Some of the other designs I viewed...well, I leave it to your imagination..
Prostate cancer- sometimes you have to laugh..