You can fit 235 /45/17 tyres on a 17 inch rim but 225/45/17 are a lot more common and as such cheaper. I would go with 225/45/17 and get them fitted by somebody who knows what they are doing and balances them.
Ride quality has a lot to do with tyre pressures and the tyre itself rather than just the size.
With the micky mouse tyres you have been fitting , which I have never heard of I am not surprised you have had issues. Tyres are not all the same round black circles you know.
Have a look on Tyre reviews.
Aptany tyres came 13/13 in this test .
http://www.tyrereviews.co.uk/Tyre/Aptany/RA301.htm
Superia tyres don't even get a mention on the tyre review website. Went to the home site http://superia-tyres.com/ and looked for info on the Bluewin.
All sizes of the Bluewin HP and UHP tyres are E rated for both rolling resistance and grip. But they are very quiet at 68dB .
Spend a bit more and get some decent tyres you will feel like you are driving a different car.
https://www.asdatyres.co.uk/goodyear/eagle-f1-asymmetric-3/225-45-17-91-y--eagle-f1-asymmetric-3 £80 fitted for one of the best tyres around.
Surprised these are still available assy 2 tyres
https://www.asdatyres.co.uk/goodyear/eagle-f1-asymmetric-2/225-45-17-91-v--eagle-f1-asymmetric-2 better rolling resistance and a better rim protection bead.
https://www.asdatyres.co.uk/goodyear/eagle-f1-asymmetric-3/225-45-17-94-y-xl-eagle-f1-asymmetric-3 The XL version of the assy 3. With the more rigid sidewalls rolling resistance is reduced and handling usually improves.
Karl , what's your long-term view of Asy2 Vs 3 , 2 are still selling probably because of the beefy rim protector, sometimes they're more £ than 3 .
Then we'll have your future MPS4 review .