CRM for keeping track of contacts in a constituency office?

Hi folks,

been wading through so many descriptions of CRMs but am not seeing the wood for the trees anymore!

I am going to be running a constituency office for an elected official from scratch – we're all new at this. I think a CRM is essential so we can keep track of people and organisations who contact us, there will be 4 of us in the office in total, working on different days, so person B needs to be able to see on Tuesday what person A might have discussed with someone on Monday.

We don't have a big budget for this (under EUR 50 per month really) and it would need to be GDPR-compliant.

Would be very grateful for suggestions!