Hi!
I Would not recommend wrestling with him. It can interfere with good pack structure and teach poor bite inhibition ( which is learning how to adjust bite pressure when interacting with you). Substitute tug instead, as you have been doing already.

As for playing tug, we should take into account his age. Generally puppies start losing teeth around 4 months. This may be contributing to his chompy bite. What kind of tug are you using? Something soft like. Fleece tug would be best at his age or a gutted French linen or jute tug.

Try moving around while playing tug to help prevent him laying down. Apply back pressure as soon as he bites, do not lift him off his front feet yet since this can break his teeth or cause then to fall out. If you walk around the room while playing it should keep him from laying down.
Best,Teresa