The tyre model is Boto Vantage H8 (Bob Jane own brand, I think). The rolling diameter equivalent in a 17 inch tyre would be 225/55.
As I see it, the options are basically 2: stay with 18" & try to get a tyre which works better for you (see post by cc1701) or move to 17" as proposed.
The dominant variables are sidewall connected.
One is height. Your current sidewall height is 109 mm. That's not ridiculously low profile short. Going to your proposed 225/55-17 size adds 14% in sidewall height to get 124mm. Other things being equal, I suggest that 14% would be noticeable.
Mind you, one could gain sidewall height within 18", though not as much.
cc1701's 235/50 option increases sidewall height to 117 (+7%). It does overgear the car by 2.2% but I suggest that that is a slight problem.
Another 18" option is 215/55. A bit taller at 119 mm (+9.3%) & similar overgearing of 2.2%.
Each of the 18" options would be a noticeable sidewall change other things being equal but they don't have to be.
Other variables apart from type dimensions concern the sidewall structure.
One concerns the number of plies involve from bead to bead. Usually this is one ply but on so-called "extra load" variants, it is usually two. Such variants are stiffer riding than one ply siblings. The other is the treatment of the bead area. In pursuit of having the tyre quickly transmit steering inputs to tread movements, "sporty" tyres reinforce the bead area by extra fold-up plies ("flippers") &/or wedge-shaped inserts of hard "rubber" ("fillers"). Such reinforcements detract from ride. So, even within the same tyre size, improvements can be found by avoiding XL structures &/or tyres designed to be crisp & quick in turn-in response.
The Boto is a tyre type which I would be suspicious of on "el cheapo" wet grip grounds but it is unknown to me; however, there are three things to note from its BJ "blurb". One is that it is an XL type. The second is that is is supposedly sporty. Confusingly, & in tension with the sportiness claim, it also speaks of comfort. Let's focus on the first two.
cc1701's Primacy 4 tyres come in two types in 225/50. Each is a "touring" tyre & thus is not as bead area reinforced as the Boto presumably is. Moreover, although one is an XL type, one is not. Furthermore, the non-XL type is the ST variant of the P4, a variant which is more comfort orientated than the regular P4.
In short, & given cc1701's experience, staying with 18" but moving to 225/50 Primacy ST tyres sounds like a good option. I can't think of a more suitable tyre for you within that size.
What of the other, slightly sidewall-taller (& lighter, another ride factor) 18" possibility - 215/55?
The P4 ST is again available but only in an XL variant. However, I note that Dunlop's FM800 tyre is available in a non-XL variant. If wet grip is important to you then this is a very good tyre in the wet from what I recall of a Choice test & from my experience of it at the rear of my rear-engined Renaults. I can't comment on comfort as I don't attend to that. I think that the FM800 in this size might prove to be a very good option.The option is improved by Dunlop currently offering a "4 for the price of 3" deal.
What of 17"? What's available in a "touring" & non-XL tyre of a decent sort?
The Primacy 4 ST & the FM800 are both available but not in a non-XL variant. Fortunately, a very good "touring" tyre is: Bridgestone's Turanza T005. Nothing else in this size attracts. As the T005 is sold in Europe (like the regular Primacy 4 but not the ST & not the FM800), a good suite of magazine tests is available in summary at:
https://www.tyrereviews.com/Tyre/Bridgestone/Turanza-T005.htm
Although no tests are available, some FM800 user reviews are at:
https://www.tyrereviews.com/Tyre/Dunlop/SP-Sport-FM800.htm
The Tyre Reviews site has nothing on the Primacy 4 ST variant but you could trawl the tests on the regular P4 & hunt for comments on comfort. See:
https://www.tyrereviews.com/Tyre/Michelin/Primacy-4.htm
You probably already know of it but for tyre size comparisons, see:
https://tiresize.com/comparison/
My own inclination would be to stay with 18" & try the FM800 unless 17" wheel offers fly in the door.
cheers! Peter