Yeah I would recommend a Stages. But they probably don’t make a crank arm reinstalled with the power unit on it that would fit your crank. They do take in your own crank and can most of the time put one on now, however that service is on hold.
Another option would be power pedals. Quarq (Saris) and Garmin both make power pedals. There are other companies as well. Though these might wear out over time like any pedal so it’s a bit of money to put in this system. But this might be your best option to get on power without upgrading your whole bike. Then you could transfer to any bike.