If you want a quick way of generating usable chords from single notes, Frozen Plain believes that Obelisk provides it.
This is a MIDI plugin that’s said to be very easy to use (don’t worry if you don’t know anything about music theory), taking the notes you play into it and harmonising them with others based on your chosen intervals. The resulting chords can then be sent to the synth or other instrument of your choosing.
The output can be constrained to a particular key and scale, which should ensure that the results you get will fit with the rest of your track. There are plenty of chord and scale presets to choose from, or you can make your own. You can also set up multiple channels featuring different chords, keys and scales, then flick between them with a keyswitch.
Obelisk is available now for PC and Mac. Note that it requires a VST2-compatible host, so certain DAWs aren’t supported. It costs $25 and is available now from the Frozen Plain website.