LOL... I do the same thing. At first, I would use two mirrors- the bathroom mirror and a hand-held mirror to see the back of my noggin. I've been cutting my hair so long now that I only use the mirrors for my neckline.
As seoulfully said, you can use different # guards and angle them for a taper. I use a #4 held with only the tips of the guard against my scalp for longer sides that lay down. I use the same guard only angled less for my sideburns and near my neckline. The guard will go from flush against my scalp and then to tips only in one smooth upward stroke.
Around the ears, I angle the guard sideways to help taper. Lately I've been trying to use shears completely, but it is scary. Good luck and lots of practice.
Every once in a while I like to splurge on a proper trim just to get everything back in alignment.