Here's a description of how to mount without pulling the saddle over too much, from one of my favorite books --
(this is for mounting on the left, obviously, but it's good to have a horse that is comfortable with you mounting from either side, as you might find yourself in a position where it'd be easier for you to get on from the right side)
First, make sure your horse is squared up, then stand along his/her side, facing their rear.
Take the reins and a portion of the mane, near the withers, in your left hand. With your right hand, present the stirrup to your left foot. Place your left foot securely on the tread, keeping the left side of your body and your left knee as close to the horse's body as possible. That way your knee can act as a pivot point as you swing up to mount. This will decrease your tendency to to pull the saddle off center. Bouncing two times seems to provide enough momentum, so that you can get up quickly, without twisting. Another helpful hint is not to grab the horn or cantle to pull yourself up but rather place you right hand on the off swell of the saddle (the one furthest away from you). Push off to the right and downward on the swell as you make your final rise and let your palm swivel as you swing over onto the saddle. This will help keep saddle slippage to a minimum.
This method, particularly the right hand on the swell, has helped my mounting tremendously. Took me a few tries to get used to it, but now I'm able to mount, without pulling the saddle over, and without having to crank up my cinch (I don't like to tighten my cinch much)
I'm not sure how you could relay this method to an english saddle, if you don't ride western. Thinking back though, I don't really remember ever mounting from the ground when I rode English. I feel like I always used a mounting block or got a leg up, but that was quite a while ago, so my memory could be failing me.
If you aren't physically fit though, you are going to struggle to get on from the ground without pulling the saddle over, no matter what method of mounting you use.
When mounting, remind yourself, that you want to push yourself up with your legs, not pull yourself up with your arms.
I'm pretty short, so sometimes I just can't mount a tall horse from the ground, so I'm always looking for aid in the form of fences or tree stumps, etc. And if there's nothing like that around, look for an incline and position yourself uphill from your horse (never, ever, ever mount from downhill of your horse)