For a tummy time mat the goal is for baby to lay in his tummy & strengthen his neck muscles and legs. For that you don't want bumpy things underneath him that could discourage him from staying on his tummy. I made the quilt in my avatar for my nephew to use for tummy time (4-6 weeks old to maybe 12-15 weeks). It had fuzzy washable plastic felt (the kind used for felt food). The other side was solid. Having some simple patterns combined with different materials, quilted circles and lines and a nice soft cotton batting like Warm & Plush make for a nice tummy time quilt.

I'd save the activity mat for him when he's at least 12 months and can sit and play on the mat, and move around to be able to play the different activities. At that point, another thing I'd suggest would be a Velcro flap that he can open to reveal something hidden (like peek-a-boo). Little ones love that. Just quilt the flap separately & sew one side to the main quilt once that's quilted. Boys love farm animals so you could make like a barn window/door that hides an animal.

A pocket, big enough he can put his hand in, or any of his toys.

The idea I had in my head was to put the noise making things near the edge so the middle was flat for them to lay on but there were things to spark interest

That is original! Very nice

You might also check put the ideas for "fidget quilts".

For a boy, the road quilt is it!! Add a couple of Hot Wheels and he will be in heaven!!

My grandson, about 4 years old if I remember right, was flying back East my daughter. This was before 9-11 and "airport security", when the friendly skies were still friendly. He wanted to take his cars, so she told him he could take any toys that fit in his child-size pull suitcase. BUT he had to carry/pull it himself. I'm sure everyone has already guess, slam full of Hot Wheels and nothing else!!

You can purchase a cloth, washable book that has snap balloons, a zipper thing, a laced up football, different textures of fabric (corduroy, velvet, etc.), a train with a pocket in two of the cars for cloth "people." . But I would use them for an older child.....not an infant.
I believe they are called an ACTIVITY BOOK. They are fairly inexpensive and sure not worth my time to make. (I am not that good of a seamstress).

I just want a tummy quilt with interest to maybe 6 months of age then it will be time for a Christmas more grown up play quilt.

I love this. I have been asked to make a quilt for a little princess. This gives me the idea of a road thru a fairy land on the way to the castle with lots of little adventures along the way!! thanks.

I understand what your saying. My great grandson received a teddy bear as a shower gift and one paw has crinkly stuff in it and one paw has a squeek in it. I don't know where you could buy this kind of notion but it seems they are available, at least commercially. My GGS loves to chew on the crinkly paw. (no teeth yet only 5 months)