Under the sink is the worst cabinet in the house and it is not close. It is deep, it is dark, it is damp, and there is a drain trap sitting exactly where a shelf would go.
Which is why the usual advice fails. Any product that assumes a clear rectangular space assumes a cabinet you do not have.
Work around the pipe, not through it
The trick is to stop treating it as one space. It is two narrow spaces with an obstacle between them, and once you accept that, the answer is a pair of narrow organizers rather than one wide shelf.
The Delamu two-tier organizer is sold as a two-pack for this reason: one either side of the trap, using the vertical space that is genuinely free. The dividers inside move, which matters because the bottles you store under a sink are wildly different heights.
The Madesmart two-tier solves the other half of the problem, which is depth. Its baskets slide out, so the cleaner at the back comes to you instead of you reaching past the plumbing with a torch.
Then get the long handles off the floor
Brooms and mops are the other reason cleaning storage collapses. They do not stand up on their own, so they lean, and the moment you take one out the rest go over.
Vertical is the only real fix. A wall-mounted broom holder grips handles of different widths and adds hooks underneath for cloths and dustpans. If you rent and cannot drill, the inside of a utility cupboard door or the side of a fridge cabinet is usually fair game, and worth checking against your tenancy agreement before you commit.
One thing not to buy
Tension rods get recommended constantly for under-sink storage. They work for hanging spray bottles and nothing else. If you load one, it slips, usually into the bin you just organised. Use them for spray triggers only, and let the tiers do the actual work.