There’s a company called Green Walks that picks up and takes dogs to the Heath.
I have heard good things about them from other dog owners but haven’t used them myself.
have you see rover.com? That’s how I found our dog walker. Happy to give you her details if you like but she tends to walk one dog at a time.
I’ve used green walks and can recommend. Reliable and lovely to the dog. My dog was always happy to go.