My trad confessor, who is geographically very close to me and available to me on an almost daily basis, has forbidden me to go to a sede chapel for Sunday Mass (for example, when traveling), so -- even though this other subject has not come up, I'm reasonably certain he would disapprove of my seeking out a sedevacantist confessor. Although he is no fan of the N.O. sacramental rites (especially its "Mass"), and although he doesn't even know how to administer any N.O rites himself, I'm pretty sure that if he really thought there were only the two alternatives named in the OP, he would suggest going to the least radical N.O. priest I knew, and only if I were fairly certain I was in mortal sin, and only also if I first made a perfect Act of Contrition. He doesn't believe that N.O. priests "are not validly ordained"; it's just that he has no use for the so-called theology of most of them, or their sacramental rites. He respects a few, very select N.O. priests whose theology and spirituality he knows, and who are personally holy, so if he were recommending alternatives to me, he might say, "If I'm not around, and you have an urgent need, try to go find Father __ in [name of city or parish]."
I completely trust my confessor, and he is also my Spiritual Director, so it's difficult for me to answer the question posed in the OP, which suggests independent decision making.
Being in mortal sin scares me in the first place. I hate that feeling. I've hated it every time I've been in that state. It's an ugly feeling of dread, self-loathing, and loss of intimacy with God, so I tend to make a perfect Act of Contrition if I think I even might be in mortal sin.