Why would use of the sofa make an area go bald? Polyester and Rayon vary all over the place. If it's a well-made fabric, regardless of the poly-rayon combination, I don't see why it shouldn't wear well.
We are VERY HEAVY sofa users (well, we use the sofa and our Labrador Retriever uses the sofa)! My sofa's have become stained, but never have they worn away because of use.
One thing that does cause a problem with upholstery fabric is denim. It will stain and abrade the fabric, any fabric (except possibly leather or vinyl). Some manufacturers will not guarantee their fabric or fabric protection treatment against denim damage.

I guess I was thinking that because it has a bit of a nap, areas where we sit a lot, getting up and down frequently, might show wear compared to the rest of the sofa.

No, I don't think you should need to worry about that. I think if there is a bit of a nap, you will have marks where people have sat; hand prints, brush prints, etc. It should not wear unevenly however, in my opinion. You should be fine.

My sofa fabric has nap (as did my last one) and doesn't show where people sat. It all depends on the fabric.

I took the samples back to the store today, and they told me the fabric is a "chenille." I haven't bought it yet. DH wants to go to the store with me to look at what else they have.

That is the exact fabric we have on a set of living room furniture. Only mine is cobalt blue. The furniture - sofa, love seat, two chairs and an ottoman - has held up remarkably well. It still looks new. The fabric cleans up with just a damp towel. We've had it for around ten years, most of that with little kids eating and spilling on it, without a problem.
I have put all of that furniture in my kids video game room. When we bought a sectional to have in the downstairs living room, I went with Chenille again. About the only thing that cleans up easier is leather.

We have a mossy green chenille and when we first got it, it was very obvious where people were sitting. Also showed water marks terribly. House "arrest" caused by a problem pregnancy really broke that puppy in! LOL. Now it all kind of blends together.

Chenile is a fairly common upholstery fabric, and generally holds up well. I have heard some pet owners complain about pet hair with it, but can't speak from personal experience.
Years ago I reupholstered a couch with upholstery fabric that was washable. I washed and dried it before doing the reupholstery, and then was able to pull off the seat cushions and launder as needed over the years (white couch...enough said). If the fabric you end up choosing is washable, you may want to consider this.