Any cotton material is suitable for you top piece. That was one of the things our ancestors used when they couldn't afford to purchase cloth. Depending on the project I've used sheets for material, as backing, and even as batting when whoever don't want a thick quilt.
I loved the 250 thread count. It was strong enough to hold the shape of the pieces I cut. The 250 count seems to be phased out in most stores as affordable sheets, and the 200 thread count is taking it's place.
All of my old cotton print material I've brought from stores were a lot thicher, maybe 300 thread count, only the plain standard material was 200 count. In January, before walmart brought back their material section, I went to Joanns for plain black fabric and it was so thin I could see through it, and the price had doubled. I had to use spray starch to firm it up so I could work with it. In comparision to a white sheet I brought for backing, I discovered they had a thred coult of 130.
In the end it is entirely up to you which material you want to use always considering what you want to use it for, and how you are going to finish it [machine or hand quilting].
p.s. Think, do you want to spend the time with a seam ripper taking out the hems?