6 weeks in Portugal itinerary idea

Do more than one base.
Lisbon is good, you can visit loads of places from there.
Also, Porto is a great choice, but consider a week long Douro River Cruise. if you don't want to do that, take the train up the river (tracks run along the north side of the river. Stop at Regua and Pinhao.

You might want to check out the Campo do Ourique neighborhood of Lisbon, as a possibility. I stayed there a month when I first moved to Portugal and it’s still basically the same, quiet, family neighborhood. No tourist shops or many tourists and has lots of restaurants and cafes, a small Mercado, etc. The rest of Lisbon is accessible by bus and there is a new metro station fairly close (wasn’t there 11 years ago).
A week in Porto would be nice, too. There are many places accessible by train and long distance bus. And, that’s a good time of the year IMO. Coimbra and Evora are easy for overnight stays, if you want. If you do this trip and are interested in meeting people while you are here, there is a very large women's social organization in which you could become involved. If interested, send me a private message once you know where you are staying, and I will fill you in.