-kha is a polite female suffix to sentences (-khrap for male) and should always be used in formal situations and to elders. -jaa is an informal, affectionate suffix to sentences, and can be used between friends or to younger people. "Sawasdee" is a literal spelling of the Thai word, but the ending 's' is pronounced as a stop, so the correct pronunciation is "sawat-dee". "Wat-dee" is Thai people being lazy (informal), as Thais like to shorten words xD

Sawasdee (kha or Krub )when they say It polite sentence Sawaddee, Sawaddeejaa ,Waddee ,for close friend or close person to speak.

Your own way sounds correct and polite. I think stick with that! :) I greet one friend with "wad dee", but this is only because we are VERY close friends. It'd be too impolite to other people... like saying "Eyyy wassup bro?" to people I don't know well. If any of the "s" characters come at the end of a word, they're pronounced as a "t".