Is there a reasonable substitute for nail guns when installing baseboards?
You could get something called a trim screw. They also sell them in white if you wish to match the color and not cover the hole with putty.

It sounds like you don't feel comfortable with trim nails as you might damage the surface of the material with your hammer. Quite frankly, that will likely happen if you're a novice.
A brad nailer is great for speed but if you have time then screw in a few trim screws and call it a day.
The only downside is that if you ever need to remove the trim and re-use it then you will likely need to know where to unscrew the screws. I would imagine that pulling the trim off without unscrewing the screws would damage the trim beyond re-use.