Sounds like a solid plan! I’d love to see photos when you are done.

I want to make one (or two) but, I think I’m going to make the pellets into a sort of bean bags first.

Measure and weigh the fabrics 1st for the overall blanket. Then for the remaining weight that I need, I’ll measure and divide the pellets and put into fabric squares. Like bean bags.

I’m planning to measure and weigh the fabrics to make the overall blanket/s fluffier and maybe warmer.

I laid my blanket over my ironing board or sofa and shook the beads to the bottom of the square. I then pinned a line 3/4 the way up the squares that went the full length of my blanket. (Parallel to where my stitch would be). It was time consuming but the line of pins allowed me to use my machine without any pellets getting in the way. I did the same line of pins all the way around the blanket when I was ready to add my binding.

Sand would need to be really coarse if you don’t want it to break through the seams. It will also wear the fabric down more quickly, and it becomes hot in the dryer. Otherwise it is fine to use it. People also use the aquarium gravel (be aware that it will also become hot in the dryer). Amazon sells the poly pellets, and should ship anywhere in the US.