January is a genuinely good time to go. Flights are cheap, nothing has a queue, and 14 degrees feels like summer when you've left Yorkshire in the dark.
Stayed at Yes! Hostel near Praça do Comércio. Mixed dorm, six beds, and the beds are better than you'd expect. Each one has its own big yellow privacy curtain, a plug socket, a reading light, and enough space under the mattress for your bag. I always get nervous about the whole hostel thing going in but the setup makes it feel a lot less exposed than I was expecting.
They do a hostel dinner most evenings for around €12, three courses with an open bar, and then a pub crawl straight after for another €12. The crawl runs seven nights a week and goes down Pink Street before ending at a club by the waterfront. The bars along the way are partnered with the hostel so you get discounted drinks. I went on my second night and I'll be honest, the social side of solo travel has always been the bit I find hardest. My first couple of trips I spent a lot of time eating dinner on my own staring at my phone, which is fine, but it does get old. Doing the dinner and then the crawl meant I was just dropped into a group of people in the same situation. I met a girl from Dublin at the first bar and we had plans for the next two days by the time we left. If you're someone who finds the social bit difficult, these kinds of organised evenings are worth doing even if they're not naturally your thing.
For food, go to Manteigaria on Rua do Loreto in Chiado. It's a small shop in an old Art Nouveau building and they make pastel de nata in an open kitchen behind a glass wall so you can watch while you wait. €1.50 each. I had two standing up outside on the pavement and then went back in for a third. The custard is still warm and the pastry is properly flaky, not the stodgy version you get everywhere else. There's usually a queue but it moves fast.
Castelo de São Jorge on the Saturday afternoon was good, mainly for the views over the city before the light goes. Getting back down at night is where it gets annoying. I had two Bolt drivers accept my request and then cancel while I was standing on a hill in the dark on my own. Ended up walking partway down and flagging a regular city taxi at a bus stop. Fine in the end but just worth knowing.
The metro is easy and you don't need to do anything in advance. Just tap your contactless card on the barrier on the way in and again on the way out. €1.80 a journey. No app, no ticket machine, nothing to figure out.
Spent around £600 total including flights, three nights in a dorm, food and everything else. January prices help but it's not an expensive city regardless.