I'm not sure it would help, as most print-at-home train tickets are designed for A4: the bar codes wouldn't even be readable if scaled down to receipt paper siz

I'm not sure it would help, as most print-at-home train tickets are designed for A4: the bar codes wouldn't even be readable if scaled down to receipt paper size. If space isn't a concern, laser printers are now very cheap. Unlike inkjets, they don't dry out, and if you're only an occasional user you may never need to refill the toner. Mine cost about a fifth of the price of a Little Printer.