Right now I'm doing crickets and flightless fruit flies. Should I alternate the days or give a little of both each day? I feel like the flies aren't as big as the crickets so he's not getting enough when I do them by themself.
If he is 2-3 months, I would try getting into larger insects than the fruit flies. Perhaps Black Soldier Flies would be a good option. I would even say that it could be time for medium to almost large crickets by now. Do you have a picture of the chameleon so we can see its size?
I alternate... out of laziness. It's been going well for me. Right now I have a ton of adult black soldier flies so they are getting those. In a few days when I run out, I will be feeding some stick insects because I need to thin their numbers. Then I will feed dubias until I pupate some more flies.