I've had good luck with these adapters:

Ebay/aliexpress/wallmart/etc. Plugs straight into the USB port too, and I use the same adapter for my n64 and snes.

You can get wii2hdmi adapters (it seems for $20) as you'd also be going straight from a digital-to-digital source rather than output to analogue then converting back to hdmi (with one of those little boxes).