Hello Maddison - answering here as well, just in case anyone else is reading this. Here's an overview of the rules starting April 1:
- April 1: no green pass required for regional trains (trains that travel within the same region)
- April 1-30: basic green pass (negative Covid test within past 48 hours, valid vaccination certificate or valid recovery certificate) required on inter-regional trains
Therefore, in your particular case, Pisa and Florence are both in Tuscany, so no green pass is required starting from April 1.