It has a seller image in the reviews that show it more accurately and to scale.
no, this hide is much too large, 21cm in diameter, for a 85g snake. You want a hide that's tight. Also, don't consider opaque hides, kinda defeats part of the purpose.
I always read everyone saying get identical hides for your BP I myself have different types of hides home made and store bought ones and my BP uses everyone of them.
As always .. your mileage may vary. Nothing is exact.
As for buying stuff in the UK. Use .Swell reptiles. they are by far the best. Their quick, cheap and have alot of stock. Also sell the hides your after.
Sphagnum moss will work yes. The medium yes will be to big for an 85f snake but you can stuff the one side until the snake has a tight fit. You can buy the smalls so you don't have to stuff the hides but you will have to buy mediums in a couple months so either pick up both sizes or just stuff with moss, it's up to you.
Swell is a good supplier I hear and I was going to post a link but they were out of the mediums.