I was pleasantly surprised a month or so ago to discover that Mary Evans has a preset for Boost that gives me a three column look very similar to what I am used to using. So far, it has worked very well for me. It is named preset_morecandy.scss and you can get it from her github repsoitory at https://github.com/lazydaisy/my-moodle-presets/tree/master/preset-morecandy
Might be worth a look.