The idea of "soft subjects" came from the idea of "facilitating subjects" - which was misunderstood so much (and threatened entries for more creative subjects) it was dropped. They basically only ever meant, "if you're unsure on what you should take - look at taking a few of these to make sure you open a lot of doors for university courses" and were about subjects being applicable to a broad range of degree courses, not about how "rigorous" or "hard" they were. (but of course - people wrongly took it this way)
Psychology would be fine in your case, and I imagine it would be a useful complement for law.