i play with "CLA 18px" because it works very well without needing TWBT. the thing about playing without TWBT, is that your game tiles and your text/menu glyphs are gonna be the same size. in my experience, the 24px (and greater) graphics sets end up with text that's much too big, and the 16px (and smaller) graphics sets end up with game tiles that are too small. for me, CLA kinda finds a happy medium
ymmv depending on your monitor size and resolution
the other thing about playing without TWBT is that your graphics set is limited to a similar number of variations as ascii. using something like the meph set, with its hundreds of variations and clever overlay compositing, is wasted without TWBT (alas: i love that set)
it's not clear what platform you're on or what launcher you're using, but some(?) of the launchers have the ability to update your existing worlds to whichever graphic set you choose to use. if you have one of those launchers, you can change your graphics set and turn TWBT on/off whenever (as long as you exit df first)
i used to switch between meph+TWBT (for fortress mode) and CLA-without (for adventure mode), but i got sick of having to keep two tilesets memorised, so now i just use CLA-without all the time because it works in both
i do not consider "adventuring with TWBT" to be a viable option, which is why this post is only talking about how you can do it without