The main reason why russia did not send special forces into Turkey is that Turkey is a member of NATO. I watched the russian TV video about the shot down plane where russian politic stated that if Turkey was not in NATO, our forces would be in Istanbul next day. Putin and russians are cowards. He can only kill weak ukrainins and syrians. When it comes to NATO member he craps his pants.
I would add a small detail: Russian shelling Ukraine from its territory, being sure that there will be no response.