A seam stick will help you press in really small areas that you have in doll clothes. In fact, there is no other way to press tiny areas like sleeve without one!
The largest stick in the picture was one I bought from a sewing notions store. It's a pretty standard piece of equipment any well-stocked notions department or store should have.
The two smaller ones were made by my husband. He sawed dowels in half and smoothed the edges and surfaces to make two sizes. They are tiny enough to fit into even the smallest doll sleeve.
Before he made me these two tiny sticks, I used to use a carpenter's pencil for pressing sleeves and other small areas.
This is the type of pencil carpenters and woodworkers use for marking. It's wider than a standard pencil and will work just as well for pressing as the ones my husband made.
But if you or your spouse are at all handy, you'll find making your own to be very handy.