Hi from the UK. I am a plus sized rider and ride English style I am 5 ft 7 and I ride a 13.2hh fell pony. My Saddler fitted us with 17.5 Thorowgood with changeable gullet. I have been riding in it ever since and get it checked annually for reflocking.
I like your horse and think given the right saddles you both will feel a lot better about each other. And good for you for getting back into riding its a great way to make you think about weight and size aswell has having a fantastic hobby that gets you outdoors and keeps you active and fitter.
I have nothing to say about western saddles as I know nothing about western riding.
But if it helps my instructor had me ride two x half hours a day is better than 1 hour long when you are carrying weight and starting out. And work up from there :) Keep up the riding it will motivate you in the long run :) and I am still jealous of the trail riding you get over there :(