I have double astigmatism as well. I also use glasses for reading and close up work and different ones for driving or seeing at distance. A hobby of mine is fly tying and fly fishing, for fly tying I have yet another pair of glasses with more power. For piano without glasses correction can produce double vision at the distance the score is from me, so often I look up at the score and see two notes where there should be one ( and they look to be very small notes at that), if I'm aware of this and careful I'll notice they are also blurry so that's not a real or faithful reading. My doctor told me that my reading glasses are too powerful for the distance I'm working at at the piano and to just go to the drug store and buy a pair of reading glasses one or two powers less than them and see how that goes. It will magnify the print just a bit. My normal reading glasses are impossible , the print at that distance when playing is blurry and the keyboard looks to wrap in an arch, gives a whole new meaning to the term surround sound !!
Ultimately I've come to memorizing but you have to get there first. I will try the drug store glasses though, I have not as yet. Two things are on my list for the weekend actually, to get a folder of some sort for all this sheet music I have scattered around my piano area and those glasses.
Anyway, you might check to see if that's an option for you as well. I didn't ask my doctor about drug store ( non prescription reading glasses) glasses he volunteered the info. He must think it will work in my case since I'm sure he would love to sell yet another pair of glasses to me.