The heart rate training in conjunction with power meter is a powerful tool to learn how to improve fitness.
Ride to HR Z2 and record the power for analysis. A block of 3-6 months consistent regular Z2 training should see you gradually increase power output for the same HR.
Quite a few riders use this software to gather your ride data from Strava. It provides a more detailed analysis of your training.
https://intervals.icu/
You could also sign upto some indoor training plan to keep focus over winter
