I have a Zetec S on 17s, love it, looks great, handling is brilliant and ride is fine apart from really dodgy roads. I think it really depends what you are used to. My last car an Audi A6 was on 19s and the fiesta ride isn't any worse than the Audi considering it was a massive car that was meant for its ride quality. Depends what you want I suppose, I'd always give up some comfort for looks / handling of the bigger wheels and low profile tyres. 

I have the 2011 Tit with 17''zs alloys on 205/40 and ride is good.

They only issue i always had was the road noise ( not tyre noise) the lack of soundproofing that ford use.

My old corsa 2009,if only one thing to say about it was it was a quiet drive,when it did move.

You could change to some smaller wheels with a larger profile tyre.  Other than that, not much else you can do!  Titanium suspension will be 'comfort' orientated anyway.

I've been after a Fiesta for a while but worried about the ride.  I bought a small car (non Ford) a couple of years ago, felt fine in town traffic on a test drive but as soon as I was out on the country roads it made me feel so ill!!  I had to return it the next day and ended up buying the Focus instead, mainly for the comfort.  So I know exactly the issue you're having.   

Reducing tyre pressures to min recommended will help a bit. On my titanium the pressures are 33/26 psi and max pressure is 35/46psi as you only just brought the car tyre pressures could be set wrong for your use. Which could give a firmer ride.