I had issues using Pellon with a blend. Pellon says their fusible products are designed especially for 100% cotton so I probably wouldn't use that.
Pre-wash everything and realize that different fabrics will break down at different rates so at some point the poly will start separating from the cotton & that will affect how the blend attaches to the pure cotton fabric, but as long as you're not making it as an heirloom, you should be fine for a few years.