I don't know if anyone of you has experience with the Boss OD-3, but it does pretty well as an SD-1 alternative as a boost (has more volume/output on tap), and it smokes the SD-1 when you use it as a low-gain stand-alone overdrive in a clean channel. The OD-3 sounds more natural and not as bass-shy (with the Tone knob neutral).
Of course, I still keep my MIJ SD-1 around just in case.
But ever since I modded a DOD 250 some 20 years ago, that has been my go-to boost.
After the mods, it has more output and less fizzy crunch and I added a low-cut toggle switch as a sort of Tight switch. Quite useful with humbuckers, since I beefed up the stock circuit to work better with Strats, but with a Les Paul, that added 'beef' gets in the way for high gain boosting.
Compared to a TS-9, the SD-1 already is more open-sounding/less congested mids, but my DOD 250 takes that even further. But there's a time and place for the TS-9 as well as the mids sit in a certain way that works well for leads more than rhythm IMO.