I concur.
I agree w/ Yatta & I understand why you seem to be overwhelmed, vinrem sir.
Been tweaking suspensions for ages. As adjustment options increase, so will a system's complexity....& we haven't touched on camber, caster, swaybar tuning yet.
On Polyurethane parts, true, they're more durable than your standard stock rubber bush, but comfort gets affected as the material's durometer increases. Not only that, PU requires periodic lubrication, otherwise, you'll hear all kinds of unpleasant noises. Besides, notable PU manufacturers, like Powerflex, have yet to come up w/ gen3 M3 upgrades, last I checked. They might still be in development & testing.
Should you opt for coilovers, you might need a good wrench or shop at your disposal for those frequent checks. Even that initial tune to chase that coilover sweetspot is a challenge to do in a few takes. Brand/make familiarity & experience are pluses here. Not all suspension shops know about every make & model. To cite a sample, I had to supply my trusted Hunter equipped alignment shop w/ M3 alignment specs for them to program.
Unless you're up for the adventure, learning curve, tweaking & maintenance, I'd suggest going the simple HTech route, vinrem sir. Way lesser things to worry about.
