Thumb of mitten on cirular needles?

I am knitting mittens on size 8 needles. For the thumb, pattern says to knit with dpns or 2 circular needles. I don’t have size 8 dpns and I have a 6 and an 8 circular needles. Will two different sizes work?

Should be okay, just don’t pull the sts too tight when you’re working on the 6 and it helps if you don’t do the same set of sts all the time on that one.