The most you can reasonably commonly use is 128k and even then, pretty much only in a IIe... The closest thing to standardisation the IIe ever saw was the extended auxiliary slot 80-col, and there's very little software out there that knows what to do with more, even when presented with it in that manner ... and even less that knows what to do with a non-aux-slot memory card.
Also, even if the II+ had the architecture to be able to extend memory in that manner, you'd come up against the requirement for a 65C02 which pretty much coincided with the extended 80 col becoming common.
Most memory extensions for the II+ are an extension of the "language card" idea from memory. Most copied a design from "saturn". (which is probably what you had in your II+) Apple's implementation was known colloquially as a "slinky" but I'm not 100% sure how it worked or if it was an "extended language card". (My "slinky" is still shrinkwrapped, and I haven't read the docs yet)
This was another idea that was close to "standard" but again, not much knows how to use anything but the normal 16k of RAM provided in the standard Microsoft/Apple "language card".
Get a language card for definite, if it doesn't have one .. but beyond that... To be honest, you're wasting your time unless you have something very specific in mind, or are planning on writing it yourself. Usually the best you can do is to find the "Appleworks" driver for the card itself and get a larger desktop ramdisk... but I'm picking your Apple II isn't your main word processing platform these days.
"dsakey" on trademe. Apple II's are my thing.