My raised bed dries within a day

Too much drainage and no mulch. Compost raises water retention, and a few centimetres of mulch on top cuts evaporation by roughly half. Both are cheap; the mulch is the one people skip and the one with the fastest visible effect.

Yes: do the first step, skip the automation, and revisit in a month. Most of the value is in the first step, and most of the cost is in making it repeatable before you know it is right.