Please don't cut his coat off to stop him getting hot! It doesn't work like this, a cat with long hair stays cool because of the vacuum effect of the air between the coat and skin, but you do have to keep the coat well groomed to get rid of the loose hair which will block the air space.
Any professional dog groomer (well most) will also do cats, so get him done professionally and then make sure you keep him groomed. We once rescued a black Persian and he was so matted his coat came off like a sheep's fleece, and he was nearly bald. It didn't take long to grow back, and we kept it groomed as it grew and he had a magnificent coat. Dare I ask why you got a long haired cat if you didn't want to be bothered to groom him?