Please help me out with a Buttercream recipe that is not Overly Sweet.

I love Buttercream Dream from here on CC. If your buttercream is too sweet, someone suggested sprinkling in a little popcorn salt and remixing it.

I use SugarShack's buttercream recipe and have had several customers remark that they love it because it isn't as sweet as the grocery store's. Perhaps that would work.

Try IMBC or SMBC.