Burping tips?

Mary

I have a 9 week old who typically falls asleep while nursing. We try to keep him upright after for 20-30 mins due to some reflux but he rarely burps. However once we put him down to sleep, within 5-10 minutes he's grunting and fussing because he needs to burp. Sometimes we go in which wakes him up and sometimes he spits up which wakes him up because he's wet.

Any tips for burping a sleeping baby?