if he respects you and it sounds like he does he will now wait for an invitation from you which is what you set up yourself. so put on your big girl panties when the time is right and either say "i'm ready for alittle more" as you're making out with him or take his hand and guide it to your breast while you're making out with him. Just because you put his hand on your breast doesn't mean you're giving him an invitation to do whatever he wants with you and it sounds like he's a respectful guy and he'll know that but if you feel the need to clarify then just say "when I'm ready for something new I'll let you know"
It's only a hard situation because you're denying the two best ways to get him to touch them. Either tell him "You can touch my boobs, I don't mind now." or take his hand sometime and place it on them.
You want him to touch your breasts, but you do not want to have sex with him? Lady, this is a perilous situation. If you truly wish to go down this path, then I suggest you have a wardrobe malfunction and take your time about fixing it.
I would say just direct his hands when things are hotting up, but you already said you didn't want to do that. I guess he could see it as an invitation for sex if you direct him to it, at least he may think it's going that way.
tricky one, you can just ride it out and see what happens in the long run or just talk to him. I presume you are both fairly mature since it's 18-24 question.