Books do benefit from a controlled environment, but for relatively short times (a few decades), they won’t be badly damaged by the temperature in a house loft (unless you’re in a really bad part of the world, perhaps). So you may be overestimating the problem. But older books might be more fragile if they’ve not been made to more recent specs.
However, the good news is that passive cooling techniques exist and are increasingly being used in building design. Typically you need a heat chimney to force convection to draw fresh (cooler) air in from below.
A low-tech example would be a black slate roof, with good vents at the top to allow heat out, and vents into the building below to allow it to draw fresh air in from the building below.
However, in winter, your requirements are reversed, and you’ll need to close the roof vents and allow warm air from the rest of the house to heat the loft.
You’ll also need to consider where the insulation is placed. In the U.K. a “cold roof” is the standard design (insulation between the top floor and the loft space, so the loft space is almost at outside temperature in the winter, and gets fairly hot in the summer). Moving the insulation to the roof instead will protect the loft against the extremes of temperature.
Moisture is harder to control; wrapping the books suitably would be the best solution. Waxed Paper, leather, waxed cloth, or similar would probably suffice.