Essential features are the ones needed for your cat to use the furniture comfortably and for you to install and maintain it correctly. These include suitable usable dimensions, clear capacity information, workable access and an appropriate footprint. A cat that needs straightforward low-level access makes that an essential requirement for your purchase, even if another household would not. Optional features depend on preference: a particular colour, decorative shape or extra toy may be enjoyable but should not compensate for a cramped bed.
Write down your non-negotiable requirements before browsing, then keep desirable extras in a separate list. This helps when a visually appealing product creates pressure to compromise. Review the list against actual behaviour rather than imagined use. A feature can move from optional to important if it addresses a clear need, but the decision should remain grounded in the cat and the home rather than the length of a product's feature list.
Use a pass-or-fail check for essential requirements before comparing preferences. If a product cannot meet the documented capacity or required access, an extra toy, attractive finish or additional small bed should not offset that shortfall in a points score.
For product comparisons alongside this advice, see Ultimate PawHouse and Taj-MeowHall. The details below explain their sizes and uses.
Further reading: giantpaws.co.uk.
Ultimate PawHouse
Taj-MeowHall
Cat-Cave