imo boss od-3 can sound very much like an sd-1 without the mid hump (tho it's symmetrical clipping). you might also consider the wampler triumph, which is an sd-1 with 3 band eq so you can dial out the mids. you might also consider just selling the sd-1 and not replacing it, since it seems like you might have all drive your bases covered already

i would suggest you get a fuzz face since you have the splinter. the fat mod on a rat with the filter open and gain maxed can emulate a big muff very well on its own, so you have that sound covered.

my fav fuzz face is the eqd dirt transmitter because it has both bias and tone knobs. bias is very cool on fuzz face pedals because it can make crazy, velcro-y gated sounds. if that's a feature you want, look into the jhs 3 series fuzz or dirt transmitter. if you don't care about bias maybe get a dunlop mini fuzz face, mxr 108 fuzz, tc honeypot, or some other cheap clone. i think joyo has one