As a small guy doing kickboxing I'm having the same issues as you they taller and heavier.

If he's long and he teeps you redirect the kick throw him off balance and come over with a overhand.

Naturally where he can jab u you most likely can leg kick him. Your longest weapon to his nearest limb. Even if u get a punch, as soon as he disengages kick his leg. The first one won't hurt him but overtime it will wear out his leg and Footworks so his punches gonna become less heavy.

U could slip his jab and throw a overhand. It's hard for the taller guy to read overhands since they come from a weird angle when your opponent is shorter.

Idk that's some shit I use. I hope it's useful to u.