I have used those type stirrup leathers on my aussie before, and I hate
them. I use the aussie leathers that are like the English leathers, except they are 3in. Wide, and don't pinch as much. I also am considering getting a pair of children's leathers because I am 5'3" and the adult leathers are as short as I can make them, which is a fine length, until I want to do more active riding.
I had my Aussie custom made for my old horse, they used the smallest tree they make, and it was still too wide for him(he has badly atrophied & damaged muscles along his spine) When I got my new horse I asked for help from the maker in deciding if it fit him
. They were hugely helpful! I sent photos of it on my horse from different angles and they digitally drew lines over the angles they liked, where it should sit and how I could shim it if I wanted to improve the fit. Overall they told me it was a good fit and they didn't try to sell anything more to me. Australian Horse Saddles, Tack, and Clothing from Down Under Horse Saddle Supply
Down Under has great customer service people to talk to live
, Give them a call and see if they can help you(you might also want to have a look at their stirrup leather options)