As other users have said, it sounds like an Endurance Western saddle may be a good option, and it is one that we see used with some frequency for this type of riding. They tend to have a higher cantle and deeper seat than a traditional English saddle which helps with rider security, and there are generally more areas to clip on any equipment that you may need.
Depending on the size of the horse, the new Julie Goodnight Cascade Crossover could be a great option, it has a nightlatch for extra security for the rider, doesn’t have a horn, and has lots of places to clip any equipment you may need. However, this saddle does not use English stirrups.
For English stirrups, there are Tucker Endurance saddles like the T49 and 249 that have English stirrup leathers, they also have lots of rings and are available in an extra wide fit, but these are not available in a synthetic material.
For a Cordura or synthetic option, the 6916 High Horse Highbank saddle doesn’t have a horn, has good seat padding, and lots of clips, but again, doesn’t use English stirrups.
A big concern here would be fit, if you send tracings to us we can definitely take a look and see if we can make a recommendation on tree fit for this new horse. You can find instructions on that here: https://tuckersaddlery.com/products/measuring-your-horse/