Welcome 19edna. Hope you enjoy your time on the forum. I find it interesting and informative.
Emilym, The most important considerations are the amount of sunlight and the kind of soil. If there isn't much sun and the soil is very dry and crumbly, then you will have a limited choice of plants. If the soil is like this, or is heavy clay, you can improve it with compost, manure and if necessary added topsoil, but you probably can't change the amount of light. In these circumstances, a raised bed makes sense if it will provide better soil, added by you, and lift the plants up so they get more sunlight. If you choose the wrong plants, they will not thrive. I hope you have a wonderful time planning and completing your border.