If you're really interested in "good functioning wires" you should stay with OEM.
The ignition electronics are subject to failure with ill applied aftermarket substitutes. You might could save a few bucks with some parts but then lunch the whole system.
***
When I did my conversion, I used solid wire core also...same as OEM. And the particular wires I used are 7mm, again same as OEM. Larger sizes can be used but they have to be trimmed at the coil to fit, and more difficult to get through the boot if you want to use the OEM boot.