I bought one of these recently:
https://www.screwfix.com/p/croydex-michigan-soft-close-with-quick-release-toilet-seat-thermoset-plastic-white/274jj
and am very pleased with it. It OK on all your points. They have improved the attachments while leaving them adjustable. First it includes a spacer bar / jig so you can set the fittings without the seat attached. Secondly they have added pads of high-strength adhesive foam like 3M VHB. When I saw this I thought it was a bad idea because you only get one chance placing it in contact. But they have a clever design with collapsible spacers. These allow you align everything with bolts finger tight. Then as you tighten the bolts the spacers collapse and the base of the fitting is stuck down. Seat cost £35 so not cheap but not the most expensive. Got SWMBO approval too.
Avoid any seat that says thermoplastic…
Robert.
Edited By Robert Atkinson 2 on 31/07/2023 12:48:36