Not really sure what your budget or needs are, but a palm sander (also called corner or detail sander) might work for you. They are relatively inexpensive and the sanding pads are too. I've used a Harbor Freight one almost daily for many years for many different types of projects.

Here's a decent one from Amazon

Whatever sander you decide on, an essential add-on is a gum rubber sandpaper cleaner. I went for years always replacing the sandpaper when it got clogged until I discovered that I could clean them over and over, and save a lot of money.

Hope that helps!