Do any DVDRs currently work on your Wii, have you tested any make at all yet?
If so, and they work, then buy the cheapest smallest set of the above and try them.
I buy unbranded Ritek DVD-R G05s, cheap as chips, burn at 20x+ and no coasters, all this buy the best most expensive brand and only burn at 2x is hogwash, old wives tales, urban myths, perpetuated by the uneducated, there is no technical specification or reason why burning at 2x or 20x is any different, and when someone shouts that it is, ask them for the spec sheets to back up their theory.
It's all to do with the quality of burn/writer/DVDR/Specs on your PC, not cost or the burn speed. Brand of disk can be important, but only important to you & your Wii, what works for you does not necessarily work for someone else, If you are doing loads of tasks on your PC, then your buffer to the writer will need to be managed, and so writing at a lower speed improves the buffer to your writer, if you are doing nothing on your PC except burning a DVD, then the buffer can easily be maintained at 20x+.
Trial & error for what suits you is best. Go for it. Buy the cheapest, work your way round them, DVD-R being the starting point, find ones that work for you