You appear to have done a good amount of looking and checking out what's out there. I'm not going to point you towards any particular saddle. You'll be better at knowing what you want than I could be.
Just a few things to say.
If you don't have a makers name that you can confirm is in Australia (e.g. James, Sid Hill, etc....) then they are being made some place else. Most likely someplace in Asia (e.g. India, etc.....). Most of what Australian Stock Saddle Co and Down Under sell are not made in Australia. I know ASSC was apparently having some very expensive custom ones made in CA.
Good luck getting a Sid Hill. I've heard he's gone into simi retirement and might make one for certain long time customers in Aus, but not commercially anymore. So whatever Sid Hill's are out there will what you get to select from. However there are some excellent saddle makers in Aus.
I've heard mixed reports on Asian made saddles. E.g. I've seen people praise the Kimberely and heard terrible reports on others. I would certainly avoid anything I heard bad things about, didn't hear good things about, didn't have a manufacture I could check on or especially is a knock off trying to pass as a recognised brand.
If you must have one with a horn (something I dislike about Western saddles
) I hope you don't plan to use the horn as a functioning working horn. It's for show (to make riders who love the "Western" look happy
), but it should serve for hanging things off of.
My oldest mare has a bit of a wide back (just over 9.5" Western gullet) and my wide Sid Hill Bushmaster fits her pretty well. It might be about a 1/4" too wide, but a thick pad has worked real well and I use it with both my mares.
I would not recommend a stock saddle for my favorite kind riding, (but there aren't many that I think measure up well for truly long distance riding) because it doesn't provide enough surface contact area. A little better than the Hungarian/German style saddles (AKA English), but a lot less than a Trooper (which actually is an "English" design saddle
from the Universal Pattern military saddle......go figure).
The stock saddle is great for weekend trail rides and as a working saddle. They usually have comfortable seats I could spend days riding on and if they had better weight displacement I'd certainly use them for my long distance riding. I own mine because of a mare who discovered that she could unseat a rider if she didn't want to go some place. Today she rides nicely. I've never had any horse unseat me from a stock saddle (an no horn to get hung up on
) so today it's my saddle of choice whenever I start a new horse under saddle even though I don't need it most times. I also enjoy it for trails and weekend riding.