If you're looking for a more relaxing card game, then we recommend a game of FreeCell, but if a challenge is what you're looking for, then you should give Spider Solitaire a shot. You still get to challenge yourself and develop your strategic muscles, but playing the game is a more laid-back experience than the classic card game.
Klondike Solitaire Turn One is a great alternative to the classic solitaire, where you turn three cards at a time.