I have tried a ton of different filters with my Yama, including the Hario metal/ paper combo and the Astoria wire filter mod. If you are going to spend money for an extra filter, my advice it to try and get your hands on a vintage Nicro metal filter from a Nicro Vac Brewer (usually you can find one up for auction on eBay). It fits the Yama brewer and is, IMHO, the very best filter you can find for the Yama. Over the past 10 years using a Yama and having tried almost every type of filter combo with a Yama that you can think of, I would have to say that the Nicro consistently produces the best cup of joe with minimal clean-up mess.
My second most favourite filter for the Yama is the tried and true cloth filter that comes as standard issue with the Yama. Only problem is that the Yama cloth filter will need to be washed/ changed occasionally to keep the coffee oils from building up.
DG