We are big on using our long lead ropes and stick and string for getting ready for the saddeling process. Flicking the string of the stick, or long lead (we use 12-14 ft lead ropes) over the back of the horse gets them used to the movement your arms and body will make when putting the saddle on. Also gets them used to feel of "something" going across their back.
We put the lead ropes around the horses girth area and will pull it taught with our hands. Not tight to scare the horse, but to put pressure on the area. It allows the horse to start feeling the sensation of constriction in the girth area. Holding it with your hands allows you to control how much pressure the horse is exposed to.
We also do a lot of jumping up and down by the girth area, where you would be if you were going to get on. Gets them used to seeing you make that movement. If you are able, it is a great desensatizer to jump up and lean across their back. Not stradle them, just lay across their back. For horses that have not been riden, this lets them see you from both sides (which is one thing that scares a lot of young horses). And they get to feel weight on their back. In this position should the horse spook, jump, take off or whatever, it is easy for you to just slid down and reassure the horse. We don't do this part until the horse is comfortable with us jumping up and down beside them.
When we do jump up and lay across the back, at first it will be jump up, lay across and immediatly slide off, before the horse really even has a chance to react. Then lots of rubbing to let them know that was all a good thing. Repeat. When they seem to be understanding what is going on, we will increase the length of time laying across the back, and really rub them as much as possible all over while laying up there.
If you are confident enough and feel you have enough skill you can work that up to stradeling them.
We have found that doing this really prepares the horse for the saddle and the sensations that he will be encountering.
When the horse is comfortable with this, you could incorporate some of the previous suggestions for introducing the saddle pad, saddle etcetera.
I hope you found something here you could use, and good luck