Hi Colette
Lucca a very good base (I always love basing somewhere that if we felt unenergetic one day, that merely staying there and having a wander around in the morning/evening would be enjoyable).
I've got a suggestion if you are going to day trip to Pisa. Try to avoid the usual tourist trail that goes from either train station directly to the Field of Miracles. Those routes are blighted by day-tripper tourism, mostly overpriced and/or tourist tat. The city itself is a 5-10 minute walk east from the leaning tower and is remarkably under-touristed given the hordes that descend on the leaning tower. Thus it is an easy and rewarding detour.
So the suggestion is to walk from Stazione Centrale to the pedestrianised Corso Italia, following it up to Ponte di Mezzo, then shuffling briefly north-west to to morning market around Piazza delle Vettovaglie area. Plenty of good value but tasty lunch places around here. From there, follow Borgo Stretto / via Oberdan north before eventually heading west along via Maffi to discover the Field of Miracles from a more pleasant entry, avoiding the worst of the tourist tat. Do not eat anywhere within a ~2 minute walk of the field of miracles (indeed treat pretty much all the famous Italian landmarks the same - places fat, dumb and happy on a steady flow of uncaring international tourists).
I always describe Pisa as BOTH an under the radar gem (the city) and a place blighted by mass tourism (the route to and in the vicinity of the Field of Miracles). The city has much appeal and some great churches in their very distinctive livery.
I'd also recommend the somewhat hidden Botanical gardens, pleasingly slightly unkempt, but a very nice antidote to the bustling tourism a stone's throw away. A nice place to relax.
There is more of the city beyond that to explore, but hopefully that's enough to show that Pisa isn't the grotty dump that the coach-tour / half day trip tourists describe (such people rarely actually see the city itself)
Regards
Ian