seatguru.com is where I go to check seat dimensions. Spirit has a seat pitch (the distance between rows) around 28", two inches shorter than major carriers. And few of their seats recline. You get what you pay for..

I can't fit in there - I'm 6' tall (183cm), so I fly Delta and buy their Comfort+ seat upgrade. But I'll also look at their 1st class fare, because after checking a bag and getting the upgrade, sometimes going all the way to First is only like $100 more (and the bag check is free, and you're first off the plane, and first to get your bag at the carousel).