I don't believe so - 1.25" isn't too big. But be sure to go slowly - start with a finger to get you use to the act of penetration. Once you are use to the finger - slip in a second. Once you are comfortable with 2 fingers - the glass will feel great because it's so firm and slippery - actually easier than fingers because of less drag.
I don't think it'll be too big, but it may feel too rigid and that might be uncomfortable. I personally think a more pliable material would feel better but if you like the material and feel like this will work for you, you should totally give it a try!