Afternoon naps never work for me. I've tried and failed those many times. I can get into SP through WBTB, so that's my only option.

If you ALMOST lose feeling in your hands and feet, then you probably aren't fully in SP. When I hit SP, I can't even feel my body anymore. It feels like it's gone. Perhaps wait a little longer, you might get too excited and that's not a good thing. I don't usually get imagery either, I just stop hearing what is around me and my body feels gone. That's when you can start crafting your dream or "roll into" it.

Try waiting about 5 minutes more from where you are, or count your breaths 100 more times. Chances are a couple extra minutes will tell your body that your mind is asleep.