That sounds crazy complicated for what's essentially a simple CRM. There are TONS of these available as easy-to-use SaaS, probably niche ones for this type of charity too.

Also, as usual, the software itself is rarely the problem. Maybe ask yourself why are they still on pen and paper in 2021. My guess? Major resistance to change, employees lacking IT skills, etc. Basically, you will not only have to pick a CRM but manage the organizational change, educate employees, etc.