K.H.
Hi
My son also loved Thomas when he was your sons age! We went with the wooden trains that connect with a magnet and these use the wooden track , they are compatible with the Brio track and trains aswell so you don't always have to buy the Thomas stuff. We liked the wooden trains because we found the detail to be better as they are bigger , we still have all the engines and accessories now even though my son has gone past the Thomas stage becase they are timeless toys and one day hopefully grandkids will enjoy playing with them.
Hope this helps
K.