Slim fit suits still too baggy. Help!
When you're working and a bit more financially fluid again, you can look into getting something MTM if you're still concerned about getting something that fits 100%.
Best of luck with the interview.
I think @jedwards is probably right about it not being as bad as you think. It also seems to be the case that without the resources to buy anything new or have your existing suits altered, you're sort of out of luck. Just be absolutely certain that when you sit down, you unbutton the jacket so it doesn't pile up. Otherwise, it's quite unlikely that you won't get a job based on the diameter of your suit sleeves in proportion to your arms. The interview is about you; the clothes aren't the star.
That said, I don't think that your first jump needs to be to MTM or bespoke suits to get something that fits better when you have resources for it. I'm not skinny like a rail, but am rather slim (6'1" 170) and have had the same problem with a lot of brands' "slim" fit. As our collective girth grows everyone wants to be "slim," so manufacturers vanity size the labels as they do waist sizes, etc. Calvin Klein's "slim fit," for example, is anything but. The arms are wide, armholes cut low, etc. Most line's "slim" seems to be to be a regular fit, while the classic is made roomier. Again, that's just my impression as a normal sized human being trying to find clothes that fit well. I can't find many other reasons to explain why we have a classic, slim, extra-slim, extremely-slim, and like...-so-slim-you-can't-even-imagine cut. Poke around the racks and see if you can find a brand/line that fits you better. Find a tailor who isn't just a Yes Man and will give you honest advice if you're not sure whether or not you're being a good judge of fit; these things are returnable as long as you don't alter them.
That, for after you get the job and want to upgrade. Good luck!
Brit comedian Jon Richardson pulls it off. On a one or two-button suit the jumper will be quite visible, framing the tie and shirt collar attractively in a manner similar to a waistcoat; on a three or four button suit, not so much.
This isn't the same guy - Google Image Search is being uncooperative - but this gent looks dapper as hell in his suit with jumper. I say go for it - if nobody else is doing it in your area you'll be setting the trends.