So go for one in the middle. You know the size dimensions on the one you already have, correct? On each product, EF lists all the dimensions of the product about ¾'s of the way down the screen.

You can also do a Search from the very beginning homepage as it list the dimensions, brand, material, company, price, etc you want to look at and leaves what you know hurts your girlfriend out. While you didn't mention if the longer & thicker dildoade YOU feel better, there are thrusting dildos/vibrators that you could leave off for your girlfriend but she could turn on for you. That way you aren't wasting more money buying multiple dildos if you don't have too.