Coaches on the forum can better address your plan.
Heart rate gets a bad rap. I personally prefer HR for most of my activities.
It’s important to make sure you perform the maintenance of your heart strap IAW manufacturer instructions, washing it regularly and making sure the battery is in good condition. If not, you can get some very misleading measurements.
If your watch can read HR from your wrist I would suggest you remove the strap temporarily and see if you are getting similar readings. You can also just do the count manually to be sure.
I’ve had a couple of instances where I’ve had to transition during a workout from the strap to the wrist. Training Peaks has a “fix” capability that can bridge the readings on your workout log so you can still get a good estimate for TSS of the workout.