Sedevacantist views, reject Vatican II, but attend SSPX Mass — need advice

I reject Vatican II completely and believe that all the so-called “popes” after Pope Pius XII have been heretics. I do not recognise any of them as true popes, from Roncalli all the way to Bergoglio and now Prevost. I believe the sedevacantist position is the only consistent Catholic position in this crisis.

However, I live in the UK, and the availability of sedevacantist Masses here is extremely limited. The clergy who hold the sedevacantist position rarely offer Mass every Sunday, and communication is very poor — they often don’t reply to emails or messages, and it feels almost impossible to build any consistent sacramental life through them.

Because of that, I currently attend Mass at an SSPX chapel. I believe the Traditional Latin Mass is the one true Mass, and I have no interest in attending the Novus Ordo, which the SSPX themselves also reject. I appreciate the SSPX’s commitment to tradition, and I agree with about 90% of their doctrinal stance.

The only issue I struggle with is that the SSPX still acknowledges the post-Vatican II “popes” — they resist their errors, yes, but they still recognise them as legitimate popes. This doesn’t sit right with me. How can heretics, who teach error and approve of false worship, be true Vicars of Christ?

So I’m asking for advice: is it acceptable to continue attending the SSPX for the sake of the sacraments, even while rejecting their position on the papacy? What have others in this situation done?

Would really appreciate any thoughts from fellow traditional Catholics or sedevacantists in similar situations, especially in the UK.