So I take it your condition is known to him/his family? That's what it sounds like if you're willing to purchase them while he's around. If this is the case, I would recommend that you get a tape on style adult diaper. It will provide a better fit and coverage for your frame than Goodnites will. Absorbency will be about the same, maybe a bit more for the adult diaper. Otherwise stick with what you know will work. The good news is that it's an air mattress so it is easy to clean in case of an accident. Just make sure that if the mattress has a velour top, you flip it to the side that will have plastic on top.
It is dangerous to go into battle with an unproven rifle, just as it is dangerous to go to a sleepover with unproven protection. That's why I recommend a taped style adult diaper, it's an upgrade to your Goodnites. If you're REALLY concerned, you can place a Goodnite Tru-Fit in your new diaper, and even get disposable pads to lay on in case of leaks. But that all depends on your nightly output. However, if Goodnites have been working for you in capacity and leakage protection those suggestions would be overkill.
I would NOT recommend you changing to any adult style pull-ups. They are NOTORIOUSLY bad. Especially for overnight protection. Not only that they tend to run pretty large and would not provide the most secure fit on your frame. The two brands that I would tentatively recommend though are Kroger/Rite Aid Overnight Underwear, and maybe Always Discreet.
The Kroger/Rite Aide Overnight Underwear have excellent absorbency, probably the best absorbency of any off the shelf sold in mainstream stores incontinence product. However, I am not sure that even the smallest size would fit you well. The Always Discreet offer second best absorbency than every other adult pull-up sold in stores, and I have managed to get by a night or two with them but I still don't completely trust them. The Always would probably provide the best fit for your size though as they are produced in more sizes they tend to have a closer fit. Both of these adult pull-ups are the only ones that offer standing leak guards. The rest do not.
Goodluck.