"Soft coral" is sort of synonymous with "easy".
Try to plan out what exactly you want to do long term. Because the easiest soft corals can easily take over your tank. Which isn't necessarily a bad thing, if you want the tank to be based around those corals. But if you want other corals down the line you want to take that into consideration.
Tree Corals (Kenya, Colt, Nepthea), Mushrooms (technically not softies but they are often kept with them since they like the same conditions) and Xenia if you want some cheap easy corals (although Xenia is weird, it is basically effortless IF your tank can support it). Those will over run the tank pretty easily though. The basic leathers (Sinularia's, Toadstools, etc.) and Zoanthids are pretty easy and aren't as prone to taking over.