We just have a few bookings and, last year, the Jotform service was free of charge up to a certain number of reservations. Is that confirmed also for

Yes Jotform is free, although there will be different limitations on each account plan.

You can see the limitations in the Pricing page.

Kindly check this guide to understand better about those limitations https://www.jotform.com/help/408-Understanding-Your-Account-Usage-and-Limits