Hi, Jan. I'd guess that one in 10 people who have contacted me about my autosomal DNA are seeking information about an adoption or known non-paternal event. I know it isn't easy, and that the search can be daunting. One thing I hope we all do is commit to always responding to DNA inquiries...even if we don't think we can help--or that the contact can help us--it's important to the person writing. So, please folks, always at least respond.
One thing that might help you immediately, Jan, is to create a GEDmatch account and upload your raw data from FTDNA. Not only does that give you a chance to have your data available to match against people who have taken tests from different companies, it gives you and others the ability to do a deeper dive into how and where the DNA matches. Vital for anyone doing atDNA research, but especially so for adoptees. And be sure, if you use a different username on GEDmatch, to give it permission to link to your WikiTree compact tree.
If either of your parents is living, a DNA test should be job number one. Even if your mother is deceased, you can still create a simulation of her genome if you have you father's test data, a process called phasing. That would help you screen matches to your kit to make sure they're on the correct side of the family.
Next, make a list of known, living relatives who would carry your mother's DNA; they might carry you father's, also, but you aren't after your father's line, so uncles/aunts and cousins on his side aren't the target. Prioritize the list by proximity of relationship: your mother's brothers/sisters first, their children second, and so on. What you're wanting to do is get others to take a DNA test so that you'll have enough information to do what's called "triangulation": getting enough data from multiple sources to build the bigger picture. Your DNA alone is often not enough in a search for an adopted grandparent because you're carrying, on average, only about 25% of her DNA. You'll want more relatives on that side of the family tested in order to get a better picture of that other 75%.
Also, if it were me, I'd create a WikiTree profile for your grandmother and include what facts you know. A good rule of thumb is the ol' "Five Ws," or "Burke's Pentad:" who, what, why, when, where. Explain that your grandmother was adopted; facts about location, timeframe, hospital/orphanage, whatever you know; and what steps, including DNA, you've taken in the search. That will give people wanting to help a thumbnail view: save everyone time and may foster a Eureka! moment. Who knows?
Last is simply a list of a few links that might prove informative. You've probably looked through them all, but....