First off, I'm sorry your having such a difficult time finding the proper diaper...
I myself wear 24/7 for need...and long story short, currently in a halo brace for my neck surgery...
So, I understand about fitting diapers being a hard thing...
When not in my current state...I too have some serious neurological problems...little feeling in one hand...and one foot, and some odd random places...
I've found that the only way I can get a diaper fit and taped on is to lay down when putting it on...
Lay the diaper out, place your bum on it...pull up and over...
By doing this I'm able to get everything proper, and only need one hand to do tapes, as my bum hold the diaper from moving...
So, experiment with tape on diapers...and you most likely will find a way to do them up proper...
Also, I would also suggest getting some molicare diapers...they have lines that run down wher the tapes go, and give you a visual cue as to where the tapes go...it really helps!
I wear molicare when out and about...and a onesie...they are purple after all!
Here's hoping you can find a way/position that works...as I myself have never found a pull-up to be very effective...