Re: wont stay up
No sorry large size condoms IMO are just a marketing ploy. A regular condom will stretch to go over your head, I think that is big enough for most guys, though I have never done a survey. Besides with condoms the tighter the better I think you get more feeling that way.
You just have a little psychological problem with the condom. A lot of guys have the same problem, myself included. Lucky for me I only have to wear a condom when having anal sex, since I am married. If we are doing that I am so arroused there is no way in hades that I am going soft.
One thing you may want to try is have her put the condom on as part of foreplay. If she does it right she can slip it on you and you won't even notice it is on. Use the non lubricated kind and have her start by giving you head, then while she is down there she can slowly slip the condom on WHILE she is still sucking you. The warmth, and wetness of her mouth will kind of confuse your penis and you won't even know you have it on.
My sister in law is a nurse for the health department where she lives, she even taught Hamsmacker and myself how prostitutes will put condoms on their johns without the guy ever even knowing he had it on.