Disclaimer: IANAA, please consult a professional. I can hook you up if you want, with someone who knows these things much better than me (drop a PM via twitter, we're following each other apparently)
tl;dr: Business income generated by partnerships (OE and EE) that maintain single entry accounting books is taxed at a unified tax rate of 22%. In addition, any subsequent distribution of profits is not subject to dividend taxation.
To create an OE or EE you need to have a business partner. EE is better because your partner will have limited partnership liability. The partner can be family but there are some exceptions which I don't remember (e.g. if your wife is a public servant, etc.). The catch here is that you're fully liable in case the company goes bankrupt... But that should not be a problem for companies offering services, especially IT.
The alternative, if you are sole owner, is to create an IKE. Taxation then 24% tax rate + 5% on dividends.
link (in Greek): https://www.startyouup.gr/el/a/58-eythynes-omorrythmwn-etair...
In your case there's an additional benefit. In case you decide to transfer your tax residence back to Greece, you might be eligible for up to 7 years 50% tax reduction.