In a narrow corner, the assembled width and depth matter more than the base measurements alone. A sleeping basket or angled platform may extend beyond the base, especially higher up where it could meet curtains, shelves or a window handle.
Measure available space at several heights and check the distance to the nearest walkway. You also need room for the cat to approach and turn, and for you to assemble, clean and inspect the furniture. Skirting boards can prevent a base from sitting as close to the wall as expected. If the design requires an anchor, confirm that its attachment point can reach the intended surface without forcing the tree into an awkward position. A cardboard floor outline is useful, but add a separate note for upper overhangs before deciding that a product fits.
Suppose the base is 50 cm wide but an upper bed projects another 10 cm on one side. The required width at that height is 60 cm before adding your chosen access clearance, not the 50 cm base width.
For product comparisons alongside this advice, see Linden wooden cat tower and Arbor Retreat. The details below explain their sizes and uses.
Further reading: cats.org.uk.
Linden wooden cat tower
Arbor Retreat
Floral Canopy