I'm so pleased my suggestion was valuable to you. I suggest you post a video here on the forum for us when you feel ready.
It's hard to judge posture from pictures. I thought your picture looked okay until I saw the video, and then I could see what some of the problems are. So a video would be great. Your lady friend is a great resource, as she can give you quick feedback about posture. Aim for feeling balanced and fluid in your movements. Think graceful dancing thoughts, or maybe visualize bamboo gently waving in a wind.
I am a big believer in exercise and body awareness. The exercise I gave you is actually a body awareness exercise. For others who are interested, this is a link
to that exercise.
Breathing is really important. When you play, breathe deeply and naturally. So often, when I was teaching, I noticed my students held their breath.
To develop breathing, a walking program is fundamental. Try to get in walking every day, breathing deeply, with good posture. I also do squats, flat-footed, and push-ups. I don't go all the way down with my squats or push-ups, as I'm a pretty old guy and going too far down is too hard on my joints. So I squat until my upper legs are parallel to the floor, keeping a straight back, bending slightly forward at the hips for balance. In my push-ups, I go down until my upper arms are parallel to the floor. That's nose about 6 inches from the floor.
Try to exercise enough to get slightly winded. Don't do anything that makes your joints hurt, but a small amount of mild muscle pain is okay.
I am not into weights, but I sometimes use light dumbbells and strands. Unless you're an athlete or a body builder, you don't need to do superman heroics. Before my operation a few months ago, I was doing 50 push-ups and 100 squats, and now I've recovered enough that I'm starting it again.
Pull-ups are great too, if you can manage it.
If you can get body awareness, you can develop physical poise and relaxed breathing. I think those are great for acquiring good technique.
Sorry I did not respond to the PM, especially after I had invited you to send one. But I got very busy and also realized that others might be interested too, and so I'm glad you posted here. My wife became disabled 8 months ago, and I'm her primary caretaker, and that has limited my time, making it hard for me to respond as quickly as I would have liked. But I'm keeping positive thoughts in mind for you and your progress.
Regards y saludos,