Good results first time, can't repeat

I bought the book and I think it's great. The first time I tried stretchlying on my side, I slept really well, and for the first time in 10 years, I woke up the next morning without any lower back pain, and actually feeling well rested. What an amazing feeling. But every night since then, for at least a month, I haven't been able to reproduce those results. I still wake up with a sore lower back.

My problem is that I have a really hard time assessing my position, and I don't know until the next morning whether I did it right or not. I think I've done all the steps right, and I feel ok when I fall asleep. But then the next morning I wake up with lower back pain and still feeling tired, and I just want to go back to sleep immediately and try again, but instead I have to get up and go to work and wait a whole day for another try. It's really frustrating. How can I assess my position better before I fall asleep? I have several questions:

1.) Step 2: How do I know if my pelvis is tipped forward far enough?

2.) Step 4: How can I tell if I'm lengthening my back enough, and in the right direction? It sometimes feels like my back shortens again when I relax, and I have to keep "re-lengthening" it several times until I fall asleep.

3.) Step 10: How can I tell if my back is swayed? And how can I tell if my ribcage is rotated correctly?

4.) Fig 4-6 & 4-7: How can I tell if my spine is sagging or twisted?

5.) How important is it to "balance" exactly on your side, and how do you do it? I seem to sometimes inadvertantly roll forward so I'm halfway between lying on my side and my stomach. 

6.) How firm or soft should the mattress be? How can you tell if it's firm or soft enough?

7.) Most of the time I feel fine when I fall asleep, but sometimes I feel some pressure in my mid-lower back. What does that mean? What adjustment do I need to make to correct that?

Thanks.