Well, I
did ask the fellow there at "platigo" when I spent forty-odd minutes on the phone to him, as to from what the balloon is made and he did as I recall tell me that it was natural rubber (like a condom, but heavier gauge of course) and was therefore susceptible to damage from mineral oil, which is what "baby oil" is and the "base" for steroid creams and ointments. Yes, they should warn you!
{"Baby oil" - just how do they extract it?

}
Warm water should be no problem, and any lubricant certified safe for use with normal condoms should be OK also.
I gather you are describing a process of inflating the balloon for a series of two minute periods with brief intervals between. It may well be that you
feel the stretch more that way, but I would not be sure that would necessarily be more effective (except insofar as you inflate more each time). It seems to me that using a device with such a consistent, even pressure, you would find that the initial sensation of the stretch "wears off" simply because nothing is changing. But it is not the
feeling, but the consistency of pressure that is the stimulus to growth of the skin.
I'm not saying you are doing it
wrongly however, if it is working, that is the only really important thing.