Sitting in front of the computer or a TV on a WBTB can complicate things, but it can be ok if you turn the brightness on the screen down.
But instead of torturing your body and mind like this (I know how it is I used to lay like this for about 2 hours at the most) because you really need to time the REM. I would suggest that after you feel that your body is relaxed start visualizing so the dreaming process starts and the wandering mind kicks in, and with some more knowledge of your wandering mind sensations it will will be easier to transition. But if you keep doing the lay still until something happens technique you really need to time it right.

Good luck. What you are doing can work, but it is really hard to stop focusing on the physical body and therefore you stay in the physical focus.