You don't need to buy a ring sizer if you know your size, or if you are happy to use the links I've put below for you to look at. You could simply message me the precise measurement of your finger / thumb / toe in millimetres. Otherwise, you can buy a multisizer from me, like the one in the picture, inclusive of UK 2nd class post using this listing.
Note - you might be able to get yourself measured for free if you pop into a jewellers, or even receive a multisizer for free from a larger company. There's only me at Dawn Gill Designs, and I'm not in a position to send these out for free, but I will send you one at cost.
Wikipedia has a useful comparison if you know your size, and want to compare it to what I have in stock: https://en.wikipedia.org/wiki/Ring_size
I make my rings from sterling silver wire, cutting and forming to a rough circle, soldering the join and then I form it to the correct shape and size, using hammers.
Occasionally I will make one using pure / fine silver opting to fuse the silver instead of soldering it for those people with a sensitivity to sterling.
Different hammers will give different effects. 
I have a few rings that I make and keep in stock, but mostly I like to make these to order; it will take me approximately 1 week to do so; please let me know your prefered option and give me any special instructions at the check out. I'll send you photos of it in progress.