Cellulose is very commonly chemically modified to improve solubility. The most common modifications are to build on the exposed -OH groups to make an ether or an ester. This is a rather versatile, inexpensive and non-toxic group of materials.
So perhaps a modified cellulose is what you meant when you asked for a cellulose that would dissolve in isopropanol and people just interpreted you as meaning literal cellulose.
-OH groups are hydrophilic and cellulose has plenty of them and yet is so water insoluble. My understanding is that cellulose is so water insoluble because it hydrogen bonds too strongly with itself. This may in part be because it can more easily form stronger crystals when compared against the very similar, but helical, amylose.
Randomly substituting -OHs with a hydrophilic ether or an ester can interrupt this excessive hydrogen bonding whilst still supporting water solubility. So methylcellulose with its hydrophilic methoxy groups is water soluble, but the longer ethoxys of ethylcellulose aren't.
However, ethylcellulose is soluble in isopropanol and will at least form films. Whether it can be made to have the physical properties you are after via plasticizing additives I do not know.