I had used Fitch up until recently when I upgraded to a DIY linnmon cage.
I also wanted to encourage burrowing (both my hamsters hadn't shown much of an interest) - I got the 85litre kaytee clean and cozy from Amazon (it was £21 at the time) and it has filled my cage (100cm×60cm) - almost too much substrate! And best of all, my girl LOVES to burrow in it! It's wonderful. Would highly recommend