Hi Raj
Thanks for the extra insight.
Certainly Holland is worth a look, and even outside of the big cities English is widely understood / spoken. I'd be slightly wary of Amsterdam, due to the rather vertical nature of it's buildings, meaning what (internal) steps there are can occasionally fell terrifying steep! There are others more expert than me, as my experiences are limited to Amsterdam and cricket tour to places such as Utrecht/Wageningen, plus a day trip to Keukenhof gardens (note limited season this is open). Hopefully others can chime in with good suggestions as I think this might be a very good option.
In Italy
The relative flatness of Emilia-Romagna might make Parma, Modena, Faenza, Bologna, Reggio nell'Emilia, Ravenna, etc. appealing. Bologna is the big city, but I suspect Parma and Modena would make for easier walking and Bologna could be done as a day trip. Reggio certainly has a large public park ideal for strolling, relaxing or people watching. Not being a tourist destination means that even a nice café with outdoor seating in a pleasant piazza, can mean a coffee sat down there is ~ €1.30 rather than the €3, 4, 5 or more that you might pay in touristy locations.
Verona is pretty flat too, and whilst a little more touristy than I'd like, isn't totally ruined by it. It presents a number of day trip options on the train (in Italy the simple regional trains have a single step, but the inter-city / Freccia trains have a few IIRC). The platforms typically require going under and underpass with quite a few steps but I think most have lifts (not that I've used them)
I'm discounting places where traveling via boats are an appeal, as whilst this is brilliantly easy on them when moving, I could see how a bad knee might make embarking/disembarking awkward. If you think this isn't a problem, then it does open some great options up, including classic such as Venice, or some Italian lakes, Aeolian islands etc.
Pisa - this place gets some awfully bad press, partially justified in the case of the area around the leaning tower and between it and the two stations. The supreme irony is it's often the half-day trippers that are most critical, yet it is the same people who fuel the rubbish rip-offs in those areas. Away from there though, the city itself is a little under the radar and has much to appeal on your list - some easy to access parks and charming botanical gardens (actually quite close to the leaning tower), very good / good value food as long as you stay in / around the city avoid the previously mentioned areas, or head on a short bus trip to the coast. The main street (corso Italia IIRC) is great for an early evening walk with ice-cream, busy but not oppressively so. It's Italy so cafes aren't a problem. Pisa is also a busy airport, quite close to the city, so that can work in its favour.
If driving, it opens many more places up, but also might count against many places. Driving in the countryside is generally brilliant, but in the cities and historic old towns can be horrific (and costly with congestion charges / ZTL etc.).
We've found rural Piemonte, Tuscany/Toscana, Puglia pretty easy for driving and the Veneto region east of Verona not bad either. There will be many options.
The plan sounds good, either 2 bases or one. My only thought on this would be to focus on what your arrival airport options are likely to be and work around that. With less than a week, it would be ideal to have somewhere really very close so you are relaxing as fast as possible.
regards
Ian