I also had memory issues using Webstorm+SST which I solved by:
1. Disabling all unused Webstorm plugins, chances are you'll only use a small fraction of the installed plugins, this can free up a ton of RAM. (In VSCode it's all about installing plugins, in Webstorm it's all about removing them!)
2. Tell Webstorm which folders don't include source code. In the project window, right-click on ".build" and any other non-source code folders and mark as "Excluded"
Then, actually debugging the lambda in Webstorm works without any special set up. (In a nutshell: add the npm sst start script to the "Run/Debug configurations" dialogue, add a breakpoint in the lambda, then hit the debug button)
https://www.jetbrains.com/help/webstorm/running-and-debugging-node-js.html