I don't have any advice on the pull ups because my kids never wore one. I never purchased any. I do understand that it takes some kids longer to get the swing of things at night, but all the kids I know who wet at night longer had pull-ups. I know kids can be heavy sleepers and have accidents, but if they have pull-ups, they also don't have to worry about learning to hold it or waking up to go pee.
Cut liquids out before bedtime and try not using pull ups. There may be some accidents, but knowing they don't have on a pull up might help trigger the hold it or get up response. It just takes practice.
As for boy undies...I think the greatest are cotton boxer briefs. They stay in place better under clothes and my son found them much more comfortable. Through trial and error, he liked them the best.
I'm pretty small and I came across some boxer briefs that my son had long outgrown. (At 15, he's much bigger than me). They were still in the pack, he'd never worn them and I tried them on. I wear little boys Hane's boxer briefs. I admit it. They fit my waist, they don't ride up, no panty lines.
Boxer briefs are the bomb!