Rewarding and well-paying seem to be at odds for most people. They have to choose one or the other. Honestly, I think that's unfortunate.
When I actually talk to people like that (not virtual discussions on the interwebs), what I often find is they have no idea what they would want to do to make them one whit happier if the "dream" job still requires a semi-rigid schedule of 40-55 hours per week. They're not entrepeneurial or independent enough to enjoy self-directed 40-55 hours, and they don't want anyone else demanding those 40-55 hours. So the very existence of a regular 40-55 hour week dooms them to years of misery while they try to figure how to get away from it all as soon as possible. They're looking for a life of relaxed leisure that they haven't yet earned nor were they born into. Or they're looking for a life of unguided, "when they feel like doing something" activity where they reap the rewards of fulfillment without paying the price of being dependable for the long haul.
It's interesting to note that people here pride themselves for "living off $25k per year" so they can retire early to do some rewarding job long term. Often the job they describe pays $25k per year! They could work that dream job NOW for the remainder of their lives, but for that nagging issue of being expected to actually show up when expected.
So, given all of this, does comp sci ring bells for you, or are you suffering from "green grass" syndrome? Comp sci jobs can include installing and maintaining networks, setting up/disabling accounts, managing security, design and programming, installing software and maintaining systems, etc. None of that screams, "My God, you helped a lot of people today!" I hear the same complaints from a few in every department in my very STEM-related company--and my company is full of people with advanced degrees who apparently still managed to spend years studying to do something they immensely dislike. Good pay and excellent benefits do nothing to help them along.
If "meaningful" is extremely important to you, you need to find "meaningful" in your work context, or you need to change your work context. That might mean working in a non-profit, teaching (not necessarily education), medicine, chaplain/clergy, etc, or it might just mean you need to find some time regularly to do volunteer work alongside your career. Honestly, most of the "meaningful" I find in my job could be found in many other fields of study.