I don't know if you'd have time before this interview, but I think it's always worth having a well fitting jacket in the wardrobe for dressing uo trousers, skirts and dresses.
I have odd proportions generally, and my weight around my middle/bum/hips can fluctuate over the years too.
But I have 2 nice jackets - 1 larger size, 1 smaller size - that I got altered to fit my short arms well.
I often get trousers and dresses altered as well - it is a little extra cost but can make a WORLD of difference to an outfit. And something that is "nice but not great" turns into something I wear over and over again.
I am in the same dilemma, sort of, as the OP as I have an interview next week. I tried on my stuff last night - and my "interview suit" is currently too tight (I could get away with it, if I leave the jacket unbuttoned, but I wouldn't be comfortable). So I am going with a nice sleeveless black dress that is comfortable, smart and fits well at the moment, and I have a jacket I can put over it if I need to (I am often very warm at work these days, so going sleeveless a lot, and my arms are ok for that - but it is an interview so I will probably put the jacket on going in at least).
I tend to wear a lot of
nice black/navy/brown trousers with plain poloneck jumpers and a statement necklace
trousers with plain tops, necklace and a plain jacket to match either trs or top (or I have a couple of patterned ones to go over a plain black top/trs combo)
a couple of skirts to wear with different jumper/ top & jacket combos
various dresses suited to the office environment (I'm wearing dresses a lot more frequently recently)
I have a handful of suits in the wardrobe, but have only been wearing those quite infrequently in the past couple of years. As long as it is smart and suited to the office, there is a certain element of more relaxed dressing in the last little while - still very corporate, but not as uptight.