A heart rate monitor is a reasonable idea, its surprising how slow you have to go to stay in zone 2 which is essentially a recovery ride.
What I started doing is picking somewhere with a good view, place to chill, or coffee shop around 5-10km away, ride there, chill for a bit, and then cruise home, so the purpose isn’t the ride itself but to chill for a bit, rather than cover as many kms as possible in the shortest time. After doing that for a few weeks, it became habit, to the point I now feel like i’ve wasted my evening if i don’t fit that in on days when i’m not doing proper rides. Sometimes now that even becomes my preferred ride and I push it a bit on the short climbs. Will see if that continues once the weather turns.