I think it's all in the mind...
Prescription ED meds help (I use them) but the best boner I ever get is with one particular WG.
On paper, she's not my type, a bit too porn star, but she's intelligent, natural, her place is warm, safe, discreet. She's professional, has a great touch, safe sex, in it for the money, uncomplicated and always answers the door dressed for the occasion. And she can put a condom on with her mouth and always has the right size for me.
I've already got a boner when I walk in and she only has to touch my cock and it's up and twitching like an 18 year old (I'm 55)
That doesn't happen elsewhere and I've often lost a boner and had condom droop. So, my view is that it's all about being totally relaxed, rather than much else.