If the repairs get tedious, for small wheels, The 3 & 5 speed take the common 3 spline cog which starts at a 13t
When Sachs supplied The 1st 3 by 2_ 6 speed to Brompton, the cogs were 3/32nd thick.. 8 speed chain ..
spare cogs are still sold (I use the 15t w a 54t chainring) they shortened 3 teeth as shift gates, but it still works as a Single .

though the 13t is also made in 1/8" by S-A ..