I'm also a heavy Obsidian user, but yes it's a full featured markdown editor.
Heynote does exactly what you like from notepad++ (persistent buffer, no saving) but instead of tabs you can press ctrl+enter and just start a new note (with line numbers starting over at 1) right below the previous one.
On top of that, hit ctrl+L and you can pick your language and get some nice formatting.
All just as lightweight as notepad/++
Yeah, but at that point you'd have to consider it against how much power the traditional banking system uses.