I have now made an end-fed Windom for QRP. For that i used the same antenna wire as to former RW end-fed antenna. The transformer and the balun is FT82-43 as ring core. For higher power use FT114-43 to the transformer and FT140-43 to the balun.
Koax between the balun and transformer is RG174, or RG58 for higher power. Also dxw 174 is good. At 1: 1 balun, I have a BNC connector. If you want to avoid a BNC connector you can proceed with RG174 cable that feeds about 6- 7 meters, or more. That gives a purchase of 20 m+ RG174. (DXW174) (RG58) .
The material I bought from Electrokit, antenna wire (Art.nr: 40110020) purchase an entire coil, it goes into other experiments, and RG174 (Art.nr: 40110174) take at least 14 m it is spent Un-Un, a. ferrite Core FT82-43 on e-bay (Italy). As the antenna wire, you can also benefit from using a wire telephone cable 1000DL.(Army surplus). You can also find good stuff at DX-Wire.de like DXW-FL and DXW-174.
I built up the unun and the transformer in 32 mm white drainpipes, yes it is actually a UnUn not balun. (Unbalanced to Unbalanced) The only tricky part is getting to the end of the tube to unun, a sitting so good that it can withstand tensile forces that arise, but something you may well resolve itself. ?