As any student of Goldilocks knows, comfort is an individual matter. What is "just right" for one isn't right at all for another. And on top of that, comfort is not a static matter. Just right, right off, may not be at all right later on. That car seat that you first sink into with a sigh of relief may leave you squirming for some serious support after a few miles.
So how is a body to tell?
I have, over years of being in and out of many cars, determined what is important to me in deciding whether or not a car is comfortable. I've devised a check list of sorts which might have some general value. Given the ultimate individuality of judgment, you can decide the relative importance of the criteria for yourself.
SEATS. I want to sit in them, not on them, but I do not want to sink into bottomless softness. I like side support on both the upper body and the thighs, so bolstering is important but should not be obtrusive. (And it is more important in cars designed for twisty-bit scooting than in turnpike cruisers.) Variable lumbar support is useful.
I want to feel no seams or welts or buttons. I like under-the-knee support and feel uncomfortable if I perceive the seat to be too short. I want a high head restraint that I can contact with the back of my head (not my neck) with a minimal of movement. I want the seat belt to be adjustable so that it will not chafe my chin or neck or bear too heavily on my shoulder.
SEATING POSITION. I want a seat that can be easily adjusted, preferably in height as well as fore and aft and rake. I personally like sitting high and upright. I don't like high cowls or high window sills. I want a "dead pedal" on which to rest my left foot without being cramped by the wheel well. I want my right foot to be equally free from encroachment. I do not mind some offset of the pedals (canting either to right or left), but such offset must feel organic to the car, not like some aberration. I want the accelerator set at an easy angle of attack so my ankle is not under tension at any throttle setting.
I want a natural place to rest my arms, whether on a pull-down armrest or some cutout in the door, but I don't want to have handles or knobs trying to share that space. I want the steering wheel to adjust up and down and maybe telescope. I want it to be fat enough to take an easy fist, and I want the spokes placed so that my thumbs can rest comfortably while I hold the wheel at 9 and 3. I do not want to feel any stitching there. I want a center horn and not tiny buttons.
SIGHT LINES. I want to see all the important instruments at a glance, none hidden behind my hands or the wheel. I want the radio above the heat controls and both understandable by feel or with a glance. I want to see where the hood ends. I want as clear a view rearward as possible and minimal blind spots. I want my mirrors larger than most cars offer.
STEERING. I want it to feel consistent and appropriate — lightest when parking, mildly resistant at high speed. I want any variable assist to be totally seamless. I want the steering to fit the car — quick for sports cars, more measured for family sedans.
RIDE. I want to have a sense of the road's surface without feeling every ripple on it. I want the suspension to be congruent with the intent of the car. Sports cars should be nimble and crisp. Small sedans sprightly. Luxury cars, well, luxurious. But still connected to the road.
GEARBOX. Whether manual or automatic, I want the ratios to be appropriate and the changes smooth. No hunting on hills. No delays in responding to the throttle.
ENGINE. I want enough low-end torque for smooth, quick pickup. Top speed is not as important to me as nimbleness at launch.
NOISE. Sound is one thing, noise another. I like to hear a throaty engine, but not a buzzy one. I don't like wind noise. Some tire noise is acceptable, but squeaks, rattles and thrums are not.
Did I choose my own car based on these criteria? Well, in a way I did. Though it is noisy and rough-riding, it is all of a package and something I'll accept in a small sport/utility.