UK seaside holiday with autistic son

[delilabell]

Hi everyone wondered if you could help with any advice or ideas.
My son is autistic. Well actually he has fasd but it has autistic adhd and spd tendancies.
We went to Llandudno the other week which he loved. We were right in the centre (good as we also have a 2yr old) the beach was great cos it was sandy but there were rock pools. There was a huge prom to run on. But I can't find anything self-catering and nice for about £800 near the centre. It was also fab cos only took 2 and a half shouts in car.
So
Does anyone know anywhere that:
Is seaside but not massively loud
Has a sandy beach
Has places that are walking distance to the beach
For about £800 for 5 days
Max 3 miles from west midlands
I know I'm asking for the impossible but this is stressing me out so much.

If a caravan park is a possibility then we loved Devon cliffs, sandy beach with a few rock pools and you can access the pool without going through the arcades. It is a large park though so might not be suitable (it wasn't too bad when we went out of school holidays and the caravans were further apart than caister). Or Swanage is nice and has a steam train

Not sure on prices but is Suffolk achievable in 3 hours? Haven at Burnham is good,, not too big, there's a nice walk up to the town, and the beach turns sandier at the town. It's quiet but plenty of places for a day out.

*not Suffolk. Somerset. (sorry to people from Somerset!)