I don't think you'll find what you're looking for, because: bigger things are bigger than small things. Full-frame cameras are bigger than APS-C cameras Medium format cameras are bigger than full-frame cameras. APS-C cameras are bigger than 1/2.3" format cameras. Just like full-sized pickup trucks are bigger than commuter cars.

I think it likely that you've been somewhat seduced by the forum-discussion-driven mystique around full frame. There's not actually anything inherently superior about that particular sensor size. Yes, it's true that twice the light gathering surface area is nothing to sneeze at. But, exposure in photography works in exponents: doubling is just one stop. (Compare going from f/2.8 to f/2 or from f/2 to f/1.4.)

If size (and price!) are major concerns, APS-C is a pretty awesome sweet spot right now, and will be for the forseeable future.

You say:

Many recommended me also the Fujifilm X100, but the fixed length makes it a little bit too much constrained in my opinion

Which is valid; having an interchangeable lens system lets you pick the lenses that best fit your usage. I'd suggest looking instead at the X-T20, which is quite compact especially when paired with the 35mm f/2 lens or another lens from that series. There are equivalent options from Sony — and even though the Micro Four Thirds sensor is a bit smaller still, Olympus and Panasonic.

You could also look at the X-T3 (which, by the way, is great for time lapses; I don't know where you got the idea that it wouldn't be). However, it is significantly bigger and heavier; you will definitely notice the difference in carrying it all day. It's a commitment while traveling; while it's smaller than some alternatives, I wouldn't really class it as an agile travel camera. For that, go with the smaller (and cheaper!) line.

All of these can produce top-quality astonishing first-class images. You do not need full frame for that. Full frame is not a magic bullet that makes cameras better. It makes them different, and it inherently makes them different in a way which conflicts with your needs.