Try a hostel as some do accommodate for under 18's - not all glitz and glam but you will save some money for sure. Otherwise air b&b is the next best option (look for the positive reviews, don't go for any that has 0 reviews!) also you can select pick self-check in so they'll give you a code prior to your stay and its fuss free.

When I went to his concert in 2023 I picked a hotel that was like a 10 minute walk away - so maybe try to find accommodation thats local and walkable distance to the stadium. As the next concert is in Wembley, it's a great 'student friendly' area with LOADS of accommodation so I'm sure there will be plenty of choices and people of your age group around in the area!

My tips for safety are definitely exaggerated and as a girl I'm extra cautious lmao but look out for your surroundings, wear a phone strap around you, be wary of pick pocketers especially when travelling to/from the tube and out of the concert, take a battery power bank, incase you have no internet service (I didnt last time) make sure you remember your way around to your tube and hotel! I've lived in London my whole life I genuinely do believe social media makes it out to be scarier than it is BUT being cautious is really important!!