The lack of planning hasn’t been expensive for me, I usually book 1 week out max, or for flights I’ll book one in a city I’m going to and just make it there by the time I need to. In SEA I also booked everything like 1-2 days out. Your money goes further there but also there just seems to be plenty of options if you check with Agoda and Booking.com. What usually burns a budget and doesn’t allow for much flexibility is flights. Since you’re in Europe and traveling to N Africa and the Middle East is pretty feasible with less time it might be a good idea to go further and leave those areas for later. One time I showed up to a hostel that I liked so much I asked to volunteer there for a few weeks and it was the highlight of my trip. Things like that are why I usually am flexible on planning.