Hi Daisy,
I think it really depends on where you're thinking about staying, and what would you like to do.
Around the Lisbon area, there are plenty of surf spots, but it requires a little travelling (either bus/train). Main beginners/intermediate spots would be
Costa da Caparica or
Carcavelos, which have plenty of schools for lessons and/or renting gear. On flat days, you can always walk around Lisbon and enjoy the city.
If you want to go outside Lisbon to the North, and stay for 5 days mainly surfing, I would advise Peniche/Baleal. There's waves for pretty much every level, and you have small relatively cheap hostels and/or surf camps that you can just go to the water by foot. There's even some hostels in Baleal where you can get in the water from the jetties, and don't even have to paddle to get to the outside, since you already enter it on the outside!
If you go down south of Lisbon, waves are usually mellower, and there are a bunch of
surf camps around Arrifana that will easily cater to your needs. Venturing even further south, Sagres is a great place, with a fare share of nice waves and surf schools.
Let me know if you need extra info!