I learned that western saddles are the best to start any horse, even future english ridding horses, because as bigger the pressure are, lower the pressure...So maybe english saddle would be to much pressure to be used at first
Baby or half pads seem to work the best because they can feel the saddle on their back
When I ride a horse for the first time, I put a very simple net with a soft bit. For saddle and girth I use a saddle cloth, which are very light and that will not bother him and then if he ever tries to nibble it is not serious :) for the strap I use A large and elastic so that her belly is not too compressed the first time I ride! For the carpet and the half pas I use classics. Even if he knows all the equipment, I prefer to put light equipment and to which I do not care more than that. You never really know what will happen for the first session :) It's better to make things gradually.
I hope this helps, bye :)