The South Coast Cycle Way is an example of a route that could work for you and allow a "static base"
The route is along the coast and has a "stopping service" that means frequent stations along the route.
You can cycle out , train back, then train out to the previous day's finish and repeat the process.
That way you get to complete a route, but fulfil your criteria.
There is also flexibility as if you are feeling good you can extend the day's trip with no fear of being overstretched