Can someone link the Me+Em palazzo trousers? I love a good palazzo (worn with loose-ish silky top and high heels which completely disappear under them, it's full-on rich bitch on me, but whatever) but when I Google I only get glorified loungewear which maybe you'd wear in a Palazzo 
Was the size right on the Sezane trousers, banana? They look a lot more fitted on the model on the website. May very well be clips in the back creating that illusion but it does indeed look very different.
If you've got the energy and time to spare it is probably worth browsing in a Cos as they do a lot of different wide-leg silhouettes so at least you'll get an idea of what does and doesn't work for you. For you, I'd predominantly look at trousers with a good fabric weight to them. I'd look for a cut that tapers slightly in around the waist, so isn't cut straight down. Don't skip over the men's section, the Casablanca trousers have that men's trouser cut with a dropped crotch to give that illusion of low rise whilst sitting at your natural waist.
Knowing that Soeur works for you, I do like the following for you from them:
Pic1: Not too far out of your usual comfort zone, but differentiating enough but less casual and more of a work trouser Pantalon Dude. Though I could totally see them work with Stan Smiths (or the Sezane coral sandals) and a looser t-shirt partially tucked in as well.
Pic 2: Quite a similar cut to the Casablanca are the Pantalon Catherine but it has a tapering detail near the ankles which gives the relatively lightweight material a weight and structure to it but it doesn't look stiff.
Pic 3: I really like these Pantalon David ones for you if you'd like to try something high waisted, a nice textured material with the dropped crotch feel but again slightly less casual. Belt not included.
Also, off the search, but these jeans, whilst an impractical white, would be a nice addition as a workwear/casual crossover pair and would work well with a lot of the more looser tops you still have and it's not a full on skinny.
Elle, it shouldn't be that hard, if it's a small gap you can get them to put an elastic in and that just pulls it flush. I've never gone down the road of altering too much but a single alteration shouldn't be too much of a challenge. Those Levi's custom fitters are popping up everywhere, I should probably have a nosy at that one but that would require me finding a nice vintage pair of 501s first. Don't tempt me!
Speaking of jeans alterations, Sock, have yours been completed by now?
Before I forget, if anyone was eyeing up something from Yvonne Kone, got an email alerting me to their sale which will start on June 9th, 17.00CET.