hostel in the summer?

[Spike]

so in a few days i will be flying to paris to start my trip off.
well im a real shitty planner and i usually have more fun when i dont plan things so i picked a few countries got myself a eurial pass and saved some money. thats about all the planning ive done. the countries i plan on seeing are france, the netherlands, belgium, luxemburg, and germany.

here is my question. i havnt reserved a bed at any hostels because i want to beable to move freely whenever i want. so will i be able to find places to sleep? or should i pack some sleeping pills to dull the pain of sleeping in the mud behind some random building?