There's lots of things you can do to help confidence jumping, gridwork is a good one as is the use of placing poles (both pretty much take care of the stride for you/horse), doing lots of flowing small courses focussing on rhythm, balance, breathing (my instructor used to make me sing my way around to force me to breathe), work on your position to feel more balanced, but personally for me the number 1 thing that works is being on a horse that naturally takes you into the jump in a forward canter, that is enthusiastic and confident and wanting to do it themselves, always looking for the next jump. When you have that feeling a few cms difference in height really becomes immaterial so long as it's within the horse's comfort zone. Like you I really can't stand the feeling of coming in to even a small jump in a half-canter that might drop to trot, chipping in little dodgy strides, threatening to stop each time etc - that destroys your confidence like nothing else IMO.
It worries me a bit that you're struggling to get this feeling from your horse and multiple instructors' solution has been spurs, without a very clear explanation to you of why, what they think the spurs will achieve and how you are to use them. If he enjoys jumping as most horses do, why are you having to nag him round the whole way, to me that needs a better explanation than 'he's lazy' or 'you're not riding well enough', plus the fact he's barely willing to raise a leg in canter on the flat indicates something isn't quite right to me. Spurs have their place but for a novice-ish person struggling to achieve forwardness and confidence that's a pretty lazy teaching solution, one step up from 'just whack him with the stick' IMO.
I hate to have to say this on every single thread but have you done all the normal health checks and are you absolutely sure he's not in pain or uncomfortable? The fact he will perk up and go nicely forward for the pro is not always 'proof' that the horse is totally sound and just being lazy, pros do tend to ride more forcefully (even if they look quiet to the naked eye) and not give the horse the option of saying no, so a stoic/obliging sort of horse will often just put up with some discomfort and appear to be going much better, but will swiftly revert to type when with a gentler person back on board. If you haven't had all this done recently I'd get his saddle fit checked, teeth done, physio out to check for any aches and pains, maybe a vet check for ulcers/subtle lameness. If all clear then maybe you need to take a closer look at yourself and your riding and perhaps take a little step back to go forwards again (I know you are already trying with lots of lessons but you know the saying about it being madness to keep repeating the same thing and expecting different results). Are you sure you're being completely effective all the time in your forward aids - I say this with all kindness and compassion, having to boot a horse constantly forwards even to raise a trot is absolutely exhausting, my legs would turn to jelly after about 10 mins of that and I certainly wouldn't be riding effectively. Perhaps ask your instructor to focus on what might be going on purely for you as a rider, or even try a mechanical horse diagnostic session? Some common issues would be ineffective or incorrect positioning of the lower leg meaning when you are giving the forward aid it's not quite coming through to the horse in the right way (lots of no stirrups work is the cure here I'm afraid!), lack of balance and 'swinging' in the lower leg, getting nervous and simultaneously giving him a forward and a 'wait' aid e.g. overdoing the half halt when he does go forward, leaning on the reins/shoulders, getting unbalanced and sitting too heavy/deep, or simply not having had the conversation with him that when you say go you expect go (but the corollary to this is that you then need to totally train yourself out of the habit of constantly using your legs to maintain the pace, it needs to be a clear leg-on aid, backed up with a schooling whip if needed, horse moves forwards in the pace and tempo desired, you then leave him totally alone, legs just passively wrapped around his sides but not wiggling, niggling or nudging unless/until he stops at which point you correct again.
The latter is pretty much the only problem I would say spurs might help you with as gives you a swifter leg back up if needed compared to using a schooling whip as you shouldn't really carry a long whip for jumping (although many people do at home) and spurs used correctly are better than a short whip as you have to take one hand off the reins to give a behind the leg tap with the latter which takes time whereas with spurs you can quickly turn your leg to the right angle to give a firmer nudge. A small pair of rounded spurs are unlikely to hurt him or fire him up out of control, but if you aren't yet mentally and physically in the habit of riding with a very still and totally balanced lower leg (no judgement, I'd say 90% of amateur riders and even some pros habitually 'niggle' and very few of us have the stability of lower leg and mental discipline to consistently use spurs correctly and as a training aid rather than just something to boot a lazy horse with) all that will happen is, in the best case he just gets desensitized to the spur same way he has to the leg and will revert to lazy type, worst case he gets totally confused and resentful about why he's shouted at to go when he's not going but also shouted at to go when he is going, doesn't understand what you want, gets stressed and/or nappy and/or tanks off thus escalating the situation further rather than helping you...