I don't have anyone to spot me, either. That's why I switched to dumbbell bench presses.
--EDIT--
I should probably add a bit more to that.
Obviously, if you ever reach your limit with dumbbells and get stuck at the bottom of your bench, you can just drop them to your sides. So it's a lot safer (and dare I say, better to be risky with when it comes to testing your limits). Thing is, because you're holding an independent weight with each hand (as opposed to one long weight with both hands like a barbell), it takes a lot more effort to keep the weight stabilized. The first time I tried benching with dumbbells, my arms started swaying a little. So it might be a good idea to start off with a lighter weight than you're used to, just so you get used to holding dumbbells.