If you should choose to go with a higher voltage battery with a regulator, take a look at this adjustable regulator/current limiter project, that was in CQ back in Feb of 2018 (I think) :

https://qsl.net/n5ib/A%20Current%20Limiting%20Accessory%20for%20QRP%20Power%20Supplies.pdf

It has the advantage of being a linear device, so no RF noise from buck/boost switchers. And has internal, adjustable current limiting to protect connected devices. The regulator is low drop-out, so needs only about 10V input to regulate at 9V.

Jim, N5IB