3 month old activities

What can i do inside when its too hot with my 3 month old to keep him occupied without holding him. Sometimes he will sit in his swing but not for long. He sleeps on his stomach so he can all ready hold hisself up pretty well, sometimes he will watch tv but he always fall asleep and i don't want him to sleep all day, and he don't seem to pay attention when i read. He likes to stand up alot anybody know the best toy for that. All ideas would be great.