I made a dog bed and I used old clothing which she dragged around with her and stuffing from old pillows and so on. Flit loves her bed. A friend whom rebuilt cars used old car seat material shredding them with scissors.

I shredded t-shirts for ours - its dense but still soft, and I throw it in the washer every week, then tumble dry. Many thrift stores have $1 tees.

I save ALL the clippings, trimmings, bits and pieces of fabric and batting as I quilt and sew. You know those pieces that are just too small for any other use. I just put them in a large plastic bag under my cutting table and when it is full, I give to a lady in our guild who uses it to make dog beds for the shelter. You just have to be careful and make sure no pins accidentily get in there. So if you have that kind of thing...use it for the bed.
This filling is soft and can be as dense as you want depending on how much you stuff in.

I like chopped foam for dog beds, you can buy it at some stores, it comes in a bag and it's shredded and fluff-able. My dogs always loved it, I would pick up their beds and give them a shake and they would be all soft and fluffy instantly. Hobby Lobby carries it and Hancock's, too, I think. It's messy, though so fill the beds outside!

assuming this is for *your* dog, use your/your family's *own* worn out t-shirts, socks, and underwear. even though you've washed them, they still smell like you to your dog, and s/he will prefer them to any other smell.

if i steal the basket (leaving the dirty laundry on the floor) and forget and let the dog in, she will rearrange the dirty laundry into her bed!

I love the idea of using old family clothing.
Kathy