I use bricks and a "Chin-Chiller." I have one Chin-Chiller per guinea pig.
I got it from forotherlivingthings.com
Chin-Chiller - For Other Living Things - Supplies For Pets
They do deliver internationally, but I don't know how much that would cost. You can also just do a quick google search for them and there are a lot of entries under shops.
My piggies love them.