If Bootstrap is taking over the web one project at a time, yours is next. Unless... you take a stand and fight for the right to develop with the freedom
not to be forced 75% of the way down the dev path before you've even begun.
At the professional web dev level, there's never been a better time to make your own stuff from scratch in HTML and CSS. Working with designers, with UX, with the product team - you can make interesting things happen on all screens.
Building from scratch, a good responsive HTML page or website template is NOT "reinventing the wheel" as many bootstrappers claim. That is nonsense. The genius of HTML and modern CSS, and their consistent operation across devices, means it isn't much work at all to create the site you want, without using framework training wheels.
The "mobile first" mantra has blown out of proportion and is now another annoying catch-phrase. It's confusing too, does it mean mobile phone first or are we talking about tablets. Or just touch screens? Does that incldue touch screen laptops?
Is there an equivalent cliche in print? "Sticky-note first" is actually a lot clearer and easier to understand.
"Mobile first" sounds like a command issued from above, with which we must obey, or perish. Next, the grid system rhetoric.
The CREDIT for responsive websites belongs to modern browsers and their consistent rendering of CSS3 and HTML. We don't need bootstrap to achieve responsive, mobile-friendly layouts. Grid layouts can be useful, but your whole page doesn't NEED to be divided into columns and rows and spans or else crumble in a pathetic heap.
Finally, the worst thing you can tell a designer is "hey, you can make it look however you like, but it must conform to the 12 column grid because that's [the way of the future; the technical limitation; how 1% of the web is doing it". Bravo, developers telling designers to keep their layout energy in their pants and conform to the grid. "Nope, those thumbs can't be flush with a zero left and right margin, it will break the grid, duh!"