You’ve probably got a couple of things going on here. I’m guessing that you’ve not ever run much. So your running economy sucks. This means it costs you a ton of energy to run even at a pace you could probably walk fast at. We see this a lot with folks coming to running later in life. To get more efficient at running you need to run more. But running pushes you HR out of the aerobic zones. You have the right idea. We use run walk progressions all the time with folks in this predicament. It’ll allow you to accumulate both running volume and aerobic training in one shot. Make the progression gradual. Start with something like 30sec run/3min fast walk for your daily routine. Do this for a week before progressing to 1min/4min then a week later go to 1min/3min then a week later 1min/2min then try 2min/2min.
We use this approach often with good success. Don’t start with this every day our you’ll likely get injured. Do this 3x/week with fast walks between and then move to 4x/week after a month. Gradual is the key word here.