Based on what you’ve said and personal experience, you might want to consider an early intervention PT eval. They can also help you with exercises and toys to promote gross motor development.

Follow momommies on Instagram she has a whole section on how to let kids figure it out on their own and only assist but not do it for them. At that age pots pans spatula a remote a wallet were the most interesting to my kid.

FYI OP, my low tone child could sit on her own at six months too. The fact that she couldn’t get in and out of a sit on her own became a flag eventually. It could be all fine and normal still, but don’t rule out low tone yet. Also low tone is not a huge deal if dealt with, so don’t stress too much about it.

I would get him something like this:
https://www.amazon.com/LeapFrog-Groove-Musical-Frustration-Free-Packaging/dp/B00MXS4UTY
Legs off for now, then put the legs on when he’s a little steadier on his feet.

OP again - also meant to say - lots of great ideas on this chain, and I appreciate it!

Maybe something like this would get him to actually stay in tummy time a bit longer:

https://www.amazon.com/dp/B01MCUJR59?tag=dotdashvwfm-20&linkCode=ogi&th=1&psc=1&ascsubtag=4173907%7Cn6fc7c181ef0848608ba26f37b9253b8b21