Buttons are easy enough to change.  A stop at your local Fabric Store or even a craft store sometimes can elicit a nice find.  Measure the diameter of the button that is on the garment already, then look at the package for a similar size.  Generally replace like with like, if the button has holes or is a shank button, you’re going to want to replace it with that.  Sewing on a shank button– I cheat, I don’t sew them on but use a fashion sized safety pin to hold them in place, If the fabric is a loose weave, a piece of tightly woven fabric square on the underside will help secure the shank button or if you are sewing on a button with holes. Generally, when sewing on a button of this type, I double up the thread, roll a knot at the end, then for each set of button holes, four or five stitches will secure the button for a long time, then I tie it off and snip the threads.