We sleep in our 4Runner quite a bit, for one or two nights at a time. In fact, the 4Runner's "campability" is one reason we bought it - it's wide enough, long enough, and flat enough back there - but just barely. I'm 6', 220 lb, my wife is 5' 3", 110 lb. I never sleep stretched out, mostly in a fetal position, so length is not an issue although width is. We use our backpacking Ultralight Thermarest pads, they are fine for thickness and softness, but the joint between rear seatback and cargo area can be a problem. You need to find a sleeping position where that lump doesn't irritate you. When we were shopping for the vehicle, we carried our Thermarest pads into the dealerships to make sure the backs of the vehicle were big enough. We also usually crack the windows a bit to ventilate our breath, but frequently around here it rains, so we keep the windows shut. Either way, plan on waking up with a lot of condensation on the interior, and on cleaning the inside of the windshield before you drive at night again. Don't forget a Thermos full of Starbucks for the morning and a wide-mouth quart pee bottle for the night!
We particularly like sleeping in "Chateau Toyota" at Whistler, where the lift tickets and food are cheap but the hotels aren't. We spent two nights in it at Whistler last New Year's - when we started the engine after coffee the thermometer was reading +6 Fahrenheit- the vehicle doesn't provide much insulation by the time morning rolls around. So a good down sleeping bag is essential in the winter. We can tell you where it's legal to park overnight at Whistler, and where to get a hot tub, towel and shower for $5 if you are interested.
We also sleep in the back before backcountry skiing in the North Cascades and at Mt Rainier, as well as on kayak trips in the San Juan Islands and Vancouver Island areas. Frankly, I'd rather live in the back of an SUV and just ski and paddle my life away, but the day job gets in the way.
Don't know about that split shelf, we don't have it. And we also don't have the third row seat option.