Thank you (and please) will never go out of fashion. Full stop. Say it simply - or take some inspiration from below.
Saying thank you is more than good manners. It is good spirituality. ~Alfred Painter
Gratitude turns what we have into enough. ~Author Unknown
Wouldn't it be an exhilarating tonic for the soul to take a moment to appreciate the simple, good things in life which are so bountiful...? ~Author unknown, c.1949
God gave you a gift of 86,400 seconds today. Have you used one to say "thank you?" ~William A. Ward
The Pilgrims made seven times more graves than huts. No Americans have been more impoverished than these who, nevertheless, set aside a day of thanksgiving. ~H.U. Westermayer