I like putting grids, to help me not to worry on the distances and can focus on my position and teaching that horse to jump higher. I like to start at around 1m and work my way up. For example with my Grand Prix horses I usually end up jumping 1.60m but I make it a bit more complicated by making the oxer wider etc. For my young horses who are still learning I usually jump about 10 cm higher then they do in a course. For example my 6 years olds jump usually in shows the 1.30m, I like to bring them up to the 1.40m doing grids. For your case. Start at around 80 and if he feels happy work your way up. It might take about 2 weeks for him to be jumping 1.20m like nothing but you will get there
So is he comfortably jumping 1m already? You might need to take it back a few steps. Set up a spread of 3 jumps all ranging in height, or even just start of with pole in front and pole behind a 90cm crossrail and ease into a vertical and increase the height.
He stops. He is a horse who must really ride before jumps. He is an insecure horse, and only jumps with those he trusts. Trying to get him up in height since the technique is good and I want to develop.