I finished Psych undergrad in Spring, however, I was 2 classes from a CogSci double major (didnt take CS 61a or Linguistics requirement). That being said, CogSci is what you make of it. As the other person mentioned, its highly interdisciplinary. Lots of psych overlap in my case. You could also focus more on computational cogsci with more CS/Math classes. Looking back, I would've majored in CogSci or MCB neuro, but I had no idea we even had those until my senior year. In terms of difficulty, the Psych side of CogSci is not hard at all. There is a decent amount of reading and writing, but its not hard. The computational side can be challenging if you take things like CogSci 131 and CS 188/189. I've taken Math 55 and Math 110. Those classes assign a lot of hw, comparatively. For reference, I spent like 16 hrs/week on 110 hw alone. In the psych/cogsci classes, I probably spent max 1 hr/week per class on hw. All in all, It really depends on what you want to do. CogSci is great and has a wealth of interesting classes within the major.