It can be tough to find a used saddle in a wider tree, at least in my world. The saddle shops are full of 20+ year old saddles on a more narrow tree than any of our horses ever needed. If you have a knowledgable trustworthy shop owner that helps, of course.
If I were in your shoes, OP, I would check horsesaddleshop and look at the partial synthetics, Fabtron, Bighorn perhaps. The customer service on that website is very helpful and they can help with fitting to the horse and then the variety of rider. They also have several pages explaining fit and the different aspects of a western saddle.
Some things I would consider in the situation-a textured or rough out seat has some grab to it. I don’t like that myself b/c you get “stuck” but for an inexperienced or occasional rider it can be a security. I also really really don’t like high “doinky” horns, they have a tendency to grab things they shouldn’t. A lower set flat topped horn is enough, IMO. The synthetic stirrups shouldn’t fight someone’s knees as badly as leather fenders that aren’t turned. Wide stirrups with taps/cages would be on a guest saddle for me and I had them on my kids’ saddles until they were very capable riders. Use a breast collar and don’t let it be floppy; get the over the neck strap if necessary to keep it in place. It doesn’t just keep the saddle from sliding back, it keeps it in place side to side for getting on/off and exciting situations. Rear cinch helps balance weight and stabilize the seat, if the saddle has a place for it, use it.
Because of all I said the fabtron easy rider trail saddle would be my pick. Some of theirs have rings so you can add saddle strings to the back. Those are fairly easy to replace from a concho but for straight out of the box that saddle would be easiest. On some of theirs I can’t see that they have a breast collar ring which is why I picked this one-I know it’s there. You could ask them.
This horn is still “doinkier” than I would prefer. On mine I will likely replace it with a flatter lower one. I slipped once getting on my horse in the mountains, muddy boots/stirrup, and my foot slid out of the stirrup just as I was up but before I had my leg over. The bottom of my zipped up vest got hung up on my doinky saddle horn as I slid down his side. Not something one soon forgets and that horse, now long retired, still gets lots of cracklin oat bran treats for not panicking that day.
My western saddle is about 60 lbs by the time all my gear is on it. This summer I’m switching to the lady fabtron after reading hundreds of reviews and first hand opinions from people I trust. It’s still a 25 ish lb saddle but coming down from 60 that is acceptable to me.