• Harp Floating Half Landing Stairs Left - $800, found under Stairs/Spiral Stairs; 4 presets, 2 recolorable channels
• Harp Floating Half Landing Stairs Right - $800, found under Stairs/Spiral Stairs; 4 presets, 2 recolorable channels
• Harp Stairs Partition 1 Tile - $175, found under Build Mode/Columns; 4 presets, 1 recolorable channel
• Harp Stairs Partition 3 Tiles - $200, found under Build Mode/Columns; 4 presets, 1 recolorable channel
• Harp Floating Stairs Up - $10, found under Stairs/Regular Stairs; 4 presets, 1 recolorable channel
• Harp Floating Stairs Down - $10, found under Stairs/Regular Stairs; 4 presets, 1 recolorable channel
• Harp Floating Stairs Partition Deco - $200, found under Decor/Sculptures; 4 presets, 1 recolorable channel
Important: The u-shaped, half-landing stairs are based on Gosik & Inge Jones' Cottage Stairs and function the same way. They use the spiral stairs' animation so they're not perfect, and they don't really have a matching cutout so you have to delete the necessary 2nd storey tiles yourself. While they're technically stackable, the same rules for regular spiral stairs apply here as well - they need to be facing the right way according to lot/world coordinates, otherwise prepare for routing tantrums galore.
I decided to add an option with regular stairs, too - you need both the Up & Down version for it to work. The "Up" goes from the lower to the middle floor, "Down" goes from the top to the middle. The floor height needs to be standard 16 steps for everything to line up. Build up your floors, place the stairs accordingly and then add the deco partition on the lowest floor. The partition has no footprint/doesn't interfere with routing.
The two column partitions also have no footprints in order not to be in the way of the stairs - sims will walk right through them if they're not blocked otherwise. I've also enabled them to be placed anywhere, including on upper floor levels' grid without the need for floor tiles underneath. They stack on seamlessly and leave no gap b/w different floors like eaxis columns do.