Bangkok

Yes, if you pick your base carefully. Bangkok has over 320 hostels on Hostelworld, group tours leaving every day and street food at around 100 baht, so being alone is cheap and rarely lonely. The costs are traffic, wet heat and evening bag-snatching from motorbikes. It suits people who enjoy big cities rather than tolerate them.

Chiang Mai

Yes, and it's gentler than Bangkok. The old city is walkable, a hostel bed starts under £10, and cooking classes, meditation retreats and elephant sanctuaries put you in a group without trying. The weak spot is the air: during the crop-burning season the smoke haze is real, so anyone with breathing problems should choose the month carefully.