First, this isn't exactly harm reduction - the best advice is indeed to stay clear off anything serotonergic while on a SSRI.
But if you've been on the sertralin for a while now, and if it stabilizes you, maybe discontinuing it just for a trip might indeed impose worse dangers than trying to combine. Primary thing about psychedelics & SSRIs is that you might feel less effects and thus subjectively (or also really) increased side effects, this applies more so to the less potent ones like psilocybin. I couldn't trip off shrooms for years now but a recent 1cP-LSD trip was the full deal off 200mcg when the other people were even taking more - admitted, I was offered it and just thought what the fuck, let's try.
DOC is a phenylethylamine and so might be more stimulating, for me this'd be the primary concern but if you know DOC and didn't get stimulatory adverse effects it'll probably be fine. Just start low, take half of your target dose, wait until full effects and then dose more if you feel it's underwhelming.
The brain unfortunately needs pretty long to fully recover after stopping long-term SSRI, some weeks probably. There's a minimal remaining risk of serotonin syndrome specially if you just started the sertraline, you might consider taking 1/4 of the dosage first to be really safe and watch out for signs like hyperthermia, tremor, agitation, high blood pressure.