Having made the transition from English to western myself fairly recently, and having tried a number of saddles, here is MY .02 on the subject.
-When you are buying online, especially eBay, make sure the seller is measuring correctly. SOme do not.
-I went from a 17 A/P to a 16" reining. Tried smaller, and it was too small. IMO, you should probably be looking at a 16.5.
-I personally like reining saddles. You sit nice and deep, and they are closer contact thatn most other western saddles.
-I also liked my Circle Y park and trail, it just never fit any of my horses well at all. However-I have friends who love them and they fit their horses beautifully (tend to be the flatter backed quater horses, from my experience)
-name brands, like Circle Y are fairly easy to resell and they hold their value well. I bought mine on eBay, had it for several years( I had bought it for my daughter) and resold it for the same price.
-I look at the saddles on ebay and horseclicks at least once a week. You will be hard pressed to find a decent saddle for $300. For that low a price, you are best off with something more local, like Craigslist or a posting in a local tack shop.
-I do recall smrobs talking about the brand she uses and recommends in another thread. I believe it was something like Caliente? You might message her and ask. They are not really very expensive at all.
-I bought mine here......Used Saddles - Shells Saddle Shack
I found her easy to deal with and very helpful. Prices are pretty good to, but then I only wanted a Rocking R (not rocking "are" like above....lol) and I love it.
Good luck in making the transition-
I am now thinking of selling my english saddle. I never ever ride in it.