@thewhitedragon69 Leyline of Sanctity might be great, since it does stop T1 kill. But it doesn't do much after T1 if you're only sideboarding it to deal with PO; if I were playing PO against White Eldrazi, or some enchantment/non-artifact based taxing deck, I wouldn't want to take the storm finish route anyway. Also, Leyline type cards usually require that you have 4 of them in the sideboard, but there are probably much more consistently effective cards that could replace them.
T1 kills are annoying, but how often does PO get to execute them? Probably much more than most other decks in the meta right now, but still not enough to use up 4 sideboard slots for a card that is dead if you draw into it, or doesn't do much after the first turn (assuming you're mainly using it to deal with PO). It's uncommon that you face 2 or 3 T1 kills in a row. So it's more likely that you win the match even after a T1 kill in a game if you have consistent hate cards, rather than ones that just slow down the first turn.
Mental Misstep could be good, since it doesn't require blue commitment to be used. It stops SDT, cantrips, Ancestral Recall, etc. FoW is probably not a good idea unless you plan to use many blue cards. Mindbreak Trap is just bad. You would probably surprise your opponent the first time you use it, but after that, they will just play around it. It doesn't stop Tinker, and would more often feed Mentor than hinder your opponent. If you run all 3 counterspells, Mindbreak Trap could be good. But then, you would want to run 3-4 of each card, which would dilute your game plan too much. Plus, at that point, why not just play a full-on UW deck, with Ancestral, Time Walk, etc?
I mostly play UB, and the hardest things to play around when facing White is early game Cavern of Souls with Thalia 1.0/Glowrider, 2.0, and a well-timed TKS. If you set them back a turn or two behind their normal pace, and you keep pumping out those creatures along with other hate pieces, they usually aren't capable of winning through them. Considering how dependent PO decks are to artifacts, if you cast Stony Silence and the like, backed by taxing effects so that it can't be countered easily, you would most often have the game in control.