Quick update:
Thank you to everybody that suggested something.
@datiswous’s X-tile is quite neat. And if it’s not exactly what I was looking for I can easily see myself using it: thx 
Following your advice, I’ll also try to find time to to leanr tiling WM, learn to use and configure it (that’s what I dread the most: the hours I’ll need to learn how to make it work like I want ;)). Instructive & encouraging video @Nicomo, thx!
@skeezmoe I don’t use KDE,sorry. But thank your for the suggestion