Belles 22a tubes

I recently picked up a Belles 22a from @indyhawg to pair with my Aragon amp and it sounds great. I prefer it to the Modwright that I was previously running in this setup. I would like to try rolling some tubes for the first time so my question for you guys is, what should I be looking for? Right now it has two Tung-Sol 12au7's in it. I keep reading that NOS Mullard is the way to go for a rich musical sound. So should I jump straight to finding a pair of those or is there something a little cheaper that will give me a similar sound characteristic since the Mullards look to be about $200 for the pair?

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