You can use any candle. You don't want to use a big candle like a seven day candle unless your planing to burn parts of the candle every mothers day. You could just use one white candle to represent both life and death since white candles can be used for anything or get two different colors that represents life and death to you. Maybe dress the candle with oils and herbs that kinda stands for motherhood like love and protection or other things you want.
I really like tea lights for remembering people. They're small, don't have to be burned for hours and are easy to find. Plus I find them less of a fire hazard that the tapers. They're not the easiest to load with oils, though. Herbs can be stuck underneath the wax puck when you pull it out of the metal container they sit in. (Hope that makes sense, heeheee).