In order to prepare, I would suggest you up the difficulty of the track you are jumping around - not just the height. Learn to adjust for half strides, how to add, how to leave one out, jumping a straight fence on an angle, inside turns, etc. Start working on these elements now over smaller courses so you are not totally overwhelmed when the jumps go up. The quickest way to ruin a scopey and game horse’s confidence is to lie to him too many times.
If you can, try to watch the good horses and riders get around at 1.15m at the shows and get a feel for the types of tracks. Would also be useful to walk a course with someone who is riding.
I see a reference to your coach being 85 - I am not sure how active your coach has been on the circuit in recent years, but jumpers, like hunters, have also changed since the good old days. Courses are a lot more technical now than in the days of the past, and really require excellent rideability to be successful.