my 14h mare is the same with any jump under 80cm! she jumps 1.20m fine though! anyway, try making the jumps interesting because he might be a little bored so use covers, buckets, anything bright and scary :) hope this helps
I have seen jumping exercises like V-poles encourage tidiness in horses. It has helped the one horse I jump with to tidy up his technique and jump more careful.
Lines also helped him, lines with longer and shorter distances.
Trotting poles will definitely also help. Try lifting them on one side as well - it ought to encourage him picking up his feet.
Trotting poles will help them learn to lift there feet. Maybe work on grid work