This is the Caminho Central that I mentioned upthread. It’s well signed and there’s a free guidebook in English and several other languages for download. The problem for
@trecile (if indeed it is a problem) is that it doesn’t connect to the CP in Lisbon, but further north in Santarém. And I also think that any attempt to create a DIY link to Lisbon would just lead to a lot of suburban road walking, which I doubt trecile is interested in anyway.
But given that the Lisbon-Santarém section of the CP is not usually very highly rated, doing part of the Central (starting perhaps from Santiago do Cacém given its historical significance and the 5-7 extra days that she mentioned) and joining in Santarém could be a good option. SdC to Santarém would be about 10 stages.