Guppyfriend Washing Bag to Reduce Microplastic Pollution
Product number: 53201 Lakeland Limited
You could use this to wash fleece, or there are the PetBags that will keep the denris in the bag to protect the machine .
If you do use fleece - you need a rough, wicking fleece (I got some from Ikea) that keeps the top surface dry and lets the pee through. You need something absorbant underneath. Don't use fabric conditioner . Use a bland non scented detergent ( I used Ecover or an EcoEgg)
I used loads of different beddings , there wasn''t one that I thought "Perfect, I've cracked it" because they all have pros/cons .
My pigs liked hay to sleep in, eat, pee in, pooh in. It gets everywhere though and needs regular changing.
I found ours needed daily changes of newspaper and hay (and fleece) . Guinea-pigs are messy but it really isn't fair on them to leave them in dirty cages . If you give them a fairly large cardbox box ( 2 doors for safety) , newspaper over a puppy pad and some deep hay , then its pretty much a roll up and replace effort .
I don't have guinea-pigs now but we kept our last three indoors 24/7 last winter from about October . They were all middle aged (nearly 5) and I didn't think it was mild enough to put them in the Pighouse . So they had huge C&C cages in the small bedroom .
Without fail, if we tried to replace the hay if they were in the cage , they'd run into it as it fell. Every Single Time 
So DD did took them out to keep watch while I did the clean.
(They aren't the sharpest tools in the shed
)