If I were in your shoes I wouldn't bother about a side hustle right now except you really need the money. Of which, even if you do get a side hustle, it might take a long time before you start realising sizeable returns from it. I would instead focus on improving my skills to make myself more attractive to my current and prospective employers. Since you spoke with higher ups, I assume that you have access within the company which is great. Even if they haven't done anything about your request yet, they know that you came to them and you can use that to your advantage in the future.
If you want to continue working in the Charity sector, find out what skills are necessary to excel there and decide on which ones most align with your current skills and aspirations. Once you've narrowed down to a particular skill, go online and find out where you can get courses and certificates for that skill.
Once you've completed the courses, go back to those higher ups and present your certificate to them. Also update your LinkedIn profile and start applying to other jobs. LinkedIn has this EasyApply feature which allows you send only a CV to an employer. Apply to as many companies as you can and see how things progress from there.