Iv got an 18 on mine and I'm afraid my legs are just not up to it, il have to work up to it , up till now iv been geared and ss is a lot harder A few quid for a used one is better in your pocket than buying a brand new one, any takers
i don't think they make freewheels bigger than 18t (they are usually 16t, 17t and 18t). there are smaller ones for bmx hubs with a different thread. maybe try getting a smaller chainring instead?
20t freewheels are available on Ebay from a number of sources. Basic ones start at about a fiver.
If anyone knows of the existence of a 19t (apart from the White Industries one), I would like to know about it as I find 46/18 on my pre-war Elswick a little high and find 46/20 a little low so I figure 46/19 would be perfection.