I've had two epidurals for two different but both difficult labours.
First was a spinal block, my baby was back to back. It did totally remove the pain, but I wouldn't recommend. I couldn't even feel contractions or any pressure. I got upset as I didn't know when to push and had a useless midwife who wouldn't tell me "you'll know" no I flipping don't, I couldn't feel if you parked a bus up there!
Second was a mobile epidural. I'd been in labour for 54 hours when this was offered (due to scarring from a previous op, scar tissue over cervix meant I couldn't dialate). I have to say this was the most amazing experience. I could feel everything but not painfully, just pressure. I could wiggle my toes, and feel the baby coming out.
It was actually funny as I told the MW one of the wires on the babies head was falling off as I could feel it coming out... but it wasn't, the baby was coming out without me pushing!
With regards to back problems, I discussed this at length with my gp and mw who both told me the link isn't between epidurals and back problems, it's with the size of babies and the pressure on backs during pregnancy. My babies weren't massive, but my bumps were and it has changed my back ever since.