Car appreciation... the aesthetics, the engineering, etc

There's no way they are 16", the smallest you'll fit on a Model Y is probably 18" due to the caliper size.

@Tenderloin If you see what size wheels and tyres you've got now, you can plug different 18" tyre sizes in this calculator https://www.willtheyfit.com/ to work out what will keep a similar diameter.

Googling suggests the standard 19" wheels and tyres are 19x9.5 and 255/45 R19.

Trying an 18x9 with a 255/50 R18 gives almost the exact same diameter (0.01% error) and a little bit cheaper cost. However, the tyres available in that size aren't as good performance as they are the Michelin Primacy 4 and I believe Tesla fit Michelin Pilot Sport 4 or 5 as standard. Tyre manufacturers won't make all of their tyre models in all sizes.

If you accept a -3.5% speedo error (acceptable to me), you could fit 255/55 R18 tyres which are a more common size due to being OEM size on many manufacturers' models. This makes them more plentiful and therefore much cheaper at £150-170 fitted rather than £250 as your current tyres are. They're also available in lots of different premium brands and tread patterns. With tyres, less popular sizes actually end up more expensive because they can't make as many of them - basic economises of scale.

With that reduced cost of tyres, you could find some nice sensible looking and more lightweight wheels, which will help with the ride quality and probably sell your nearly new wheel and tyre package and break even.

That will be the most economic way of improving ride quality, messing around with coilovers and spring rates will send you down a 3-5k warranty-voiding hole.