I usually just use my Apple watch, wear it to bed to get my HRV. I had to use a program called HealthFit to get all the different data to TP, it works great. Besides my HRV, I get sleep and weight from my wifi scale. It will work with a lot of devices including Garmin and it’s free!
The 7 hour video series is a very good intro to the methodology for any endurance sport, don’t worry about mountaineering specific at your stage of learning, and it is cheap! However you need the book as backup reference material. I watched it 3 times and referred to the book repeatedly while trying to understand the concepts well enough. This is a very inexpensive way to get an introduction to the methodology. The training plans are cheap as well. There is plenty of articles and podcasts here to help you modify one. If you can’t afford a trainer you can get there, it will just take more effort.
Now to the real issues:
I am 65 and holding mid 80’s on TP. This is after about 2 years of effort with a long history of aerobic and strength training (not always the correct training but consistent over the years). So first I would say that is an aggressive time period. I am training about 12 hours per week to keep that number. By the time my rest day comes I am beat. We don’t recover nearly as quickly. So first question is given your BMI can you really ramp up that much training while trying to maintain a calorie deficit at 60? Trying to lose 30+ pounds in 9 months (based on your original post date) while pounding out the hours is a misery and very demotivating. It will really mess up your recovery. Second, how aerobically deficient are you? You need to baseline your current AnT and see if you are within the magic 10%. If you are really deficient it could take a long time before you can start doing enough hours to really knock off 30 lbs. Unfortunately AeT work does not burn calories very fast. So you have to put in lots of hours, but you are probably not ready to do 2-3 hours a day I would guess.
You don’t really need a special plan for age, you just have to realize it is going to take much longer to get to your goals than a 20 year old. You can do it but I would say more like 2 years, not 9 months. After 2 years of work I did Aconcagua and it was a great experience. Started out with 5 other members in our group, all in their 30’s and only myself and one other group member summited. This stuff works, but over 60 just be patient and have realistic goals. Cheers