The cushions
Look out for bull-nosed edge cushions. These are seamless where the seat joins the front of the cushion, and so can be more comfortable when seated for longer periods.
Consider weather- or season-proof cushions. These vary in texture and not everyone likes the feel. However, high-quality ones are now difficult to distinguish from normal material. Water-repellant and UV-resistant to prevent fading, some contain a free-draining, ventilated core that allows water to pass through easily, giving you a dry seat within hours of a downpour.
Forgetting to bring in non weather-proof cushions means long hours waiting for them to dry out and the danger of their being put away while still damp, which induces mould.
Cushions should also have easy-to-remove zip covers, for quick and easy cleaning as and when it is needed.