It might be worth your while to get a small kitchen scale to keep track of the weight of your snake. A good way to measure how much to feed is by using a scale to weight the snake and the feeders. I feed 10-15% of the snakes body weight for snakes under 1,000g.
I am not sure how old your snake is but hatchlings can eat adult mice after about a month out of the egg. The next size up from a hopper would be an adult mouse.
I wouldn't completely give up on f/t. Sometimes babies do better on a few live feedings and after that will gladly take f/t. If he doesn't eat f/t next week, don't give up. Wait another week and try again. He could easily go a few weeks without eating so don't worry. As long as he isn't loosing a lot of weight he will be fine!