New battery for macbook pro 2012

My wife's MBP (2012) is finally showing real signs of age. I replaced the hard disc some years ago with an SSD which made everything go much faster, but now it's started to shut down without the power cable in and the cursor has become slow and sometimes doesn't move. The system prefernced says the battery needs servicing. So, I guess it needs a new battery. Except that the cycle count is only 910. It's running on Mojave at the moment and I'm wondering whether an upgrade to Catalina might help.(or perhaps bring everything crashing down!) On coconutbattery the design capacity is 67% and it says "check battery".

So, can't afford to get an Apple Battery (can you even still get them for a MBP 2012?) so need to source a cheaper though reliable one (in UK). Any suggestions re new battery (below what price shouldn't I look at?) or alternative solutions to present problem most appreciated..