I feel you Boomer.
People think it's so damn easy to transit from one stance to another, they can just do it on the fly in the ring. Wrong.
I'm having so much problem with orthodox because I've always been a southpaw (I am right handed btw).
The saying "Think in an mirror image, and you'll be fine" doesn't work.
I've always relied on going back to southpaw when things get out of hand, but recently I've pushed myself to remain orthodox because as I grow older, I can't afford trading hits anymore.
One thing you can try is to do some corner practice, and lots and lots of shadow boxing. Corner practice is when you're in the corner and need to defend yourself from a rush while unable to move away. You should be familiar with this but man it's hard when you're unable to fight in your 'natural' way.
Other than that, follow PW's words. He's older than me, he knows more. That's for sure.