I've tested those methods, but dosen't work in my case.There are several options. You could bevel everything and spread the resulting edges out to get a softer corner. Or you could manually place edge loops with tighter edge loops on the sharp corners and more spread out edge loops at the rounder area. Or you could use creases, which is you can look up how to use.
Thanks a lot!All of those methods would work fine. Here's some screenshots for the edge loop method, like Dave suggested. I wasn't going to go to the trouble, but hopefully other people will benefit from this quick demo too.