Small cell to power Arduino Nano ?

I’m working on a small data logger with an Arduino Nano. The first idea was to power it using a 9V 6LR cell but it is slightly too large and I don’t really need 9V, only 6. Another idea was to use 2 button cells but the circuit needs about 20mA and this seems to be too much for button cells. Thanks !
What cell would you use ?

Three AAAs