I agree with all of your points except the last one.
Doing anything you know your S/O would be hurt or feel betrayed by is cheating.
However, for whatever reason you need extramarital sex, or even jsut sex because she's not putting out, then see a reputable agency pro. Not a SB, indy or leolist girl. Put a Chinese Wall between you and the SP..
Adopt an alter-ego. Name, different profession, west end if you are from the east, etc. Do not admit you are married. Get a burner app or eSim second number. Do not use interac or leave any record. Set aside a cash stash in advance, a little at a time. Do not draw out $300 from an ATM when you said you were going to work out at the gym. Do not get emotionally involved, Get your sexual needs satisfied, enjoy the escape/release. and go back to your normal life. Do not become a regular, do not ask to exchange numbers etc. Keep your emotional distance.
This way, you are not risking the personal consequences that come along with seeing a sugar baby. Whether it is knowing who you are and it getting back to your S/O or you getting emotionally involved and making stupid decisions thinking with your dick.
If your marriage is really not viable, time to bite the bullet, separate amicably as possible and then move on to sigle life where getting laid and having a girlfriend is just as much as a PITA nd you will ee the. value in seeing reputable agency girls.