Cheffy, you can use just about any simple pattern or design that you want for springle molds. I have four antique rolling pin molds that are made our of maple but I have carved them in basswood as well.
For a flat press mold you will want the wood blank fairly thick, at least 3/4" to avoid warping from being washed then stored. Once the mold pattern has been carved it is a simple task to add a handle. Drill a dowel hole into the center of the top side of the press going about half way into the wood without drilling through the carving. Get a wood drawer knob and drill it out to match the dowel size. Cut your dowel pin to fit and glue it together.
Remember when you do the carving ... if you spoon carve it, you carve the image down into the wood the cookie image will be raised. If you high carve it as you normally would do a relief carving the cookie will be inverse.
The trick to springle molds in not the wood or the carving it's the dough!!! How well you have dried the dough is what determines how well the cookie presses and keeps that press during baking.
Oh ... and springles never last very long around here no matter what the design
Susan