Being big, and owning haffies with their beautiful round shape and non existent withers does make mounting an interesting time at best.
I ALWAYS mount using a block, although when I lost all the weight I did prove that I could mount from the ground, although it wasn't pretty, I will stick to the block, less stress for woman horse and tack.
Just right now, today I am struggling to go ride, simply because of my current mounting issues.
1) Last time I tried to ride Fancy, my little Haflinger, she bolted and bucked when I was half way on, dumping me on the floor, and totally shattering any mounting confidence I had. (this is some months ago now)
2) A few weeks ago I was mounting Bert when the cyst in the back of my right knee burst, causing the most intense pain, had to dismount again as soon as I could, and someone had to bring me a set of crutches, because I was non weight bearing.
SO, I was already scared by the whole, big woman pulling saddle under horses belly while she tries to get on picture in my mind, and this is now compounded by the actuality of the fact that someone MAY dump me, or my stupid knee will give out again.