I know you want to protect your pup, and Vets tend to give a specific date for full immunity, but if you haven't seen the sticky Puppy Socialisation versus Risk of Contagion

The best "Puppy Romp" I found, was allowing 1 week after first shot, and there were in the indoor hall, some very young and small puppies, with new confident older pups rapidly getting moved outside to the more boisterous play area. There wasn't any bullying of small pups that I saw inside, they were much more polite and big eyed than I expected before I went.

Sounds like you're doing great