I developed a Java application in Netbeans, and I'm going to release it soon so I'm working on making it less ugly. Since I'm developing on a Mac, the GUI builder uses the Mac Look & Feel, which looks decent, but many of my users won't be using Macs. The default L&F is Nimbus, which looks fine except for the buttons, which have annoying borders that are not overridden by the manually setting the borders (you can see how the manual borders look in the image). With the manually set borders, the Nimbus L&F adds its own odd border inside the border I made, which just looks idiotic. Without the manually set borders, Nimbus's borders overlap in visually unappealing ways, and in order to avoid overlap I have to space the buttons really far apart, which I also don't like.
I tried using the other L&Fs available in Netbeans (Metal and something else), but they're just too ugly to stand.
Basically, I would like some advice on how to customize the way buttons look in this application. I don't want to write a button drawing function from scratch or design my own images. I just want a way to change the settings so things don't look stupid. I read in various places that the Substance L&F is good, but I can't find where to download it anywhere. If someone could link me to a download page for Substance or recommend another popular, simple and not stupid-looking L&F, I would greatly appreciate it.