Hi there, I'm not sure what country you're in (I'm in Australia) but if you don't think you are getting enough PT through early intervention you can always get some private sessions as well. Our early intervention only gave us PT one fortnight and OT the next, they also offered speech therapy, hydrotherapy and play groups.
There are toys you can get if he is very fisted and has trouble opening his hands to get 'cause and effect'... they are call 'switch adapted toys', you can look them up on the internet.
You proably wont get a formal diagnosis for him until he is about 2 because there are many disorders that can mimic cerebral palsy. Has your little guy had MRI's and bloods done? Although 9% of children with cerebral palsy can have a normal MRI... my daughter was one of these.
Do you find with his tone that he is stiffest when he is unstable and more floppy when he is relaxed and feeling secure? That is how my daughter is, our OT described it as dynamic tone.
There is also Botox injections that can help with spasticity. My daughters first lot were in her hands and wrists and worked amazingly to help open them up. She is 5 now and she can do so much, she's even learning to write her name... she just does things differently.
You will probably find your little guy will benefit from the use of AFO's (ankle, foot orthosis), they help stretch the hamstring and calve, keep the foot in a good position and help them to weight bear better.
I'm glad you have a Bumbo... mine was invaluable, we used it right up until she was 5, we took it everywhere and even used it on a regular chair at the dinner table.
There is so much for you to learn and if you're like me you are going to feel bogged down by input overload, but before long you will know so much and be a wonderful advocate for your boy.
There is also a rating scale that you can check his progress on... it's called a GMFCS (look on the net)... it will give you an idea of what level his motor skills are at.
Even though my daughter is GMFCS level 4 (which basically means she'll never walk unaided) she can talk the leg off a chair, she can crawl (bunny hop), she is a social butterfly and is about to go into mainstream school.
Oh and one of the best bits of advice one OT gave me many years ago... 'don't treat her like she's different, she doesn't know she's different, just treat her like one of the kids'... and I do, she still gets chores, gets time-out if she's naughty and gets reward charts for goals.
Feel free to chat any time