I would start off with a custom-made croset. Yes they are expensive but if you are going to be wearing it mostly all day, eveyday you want to be as comfortable as possible. Also, you should be able you get your corset resized once you start losing inches.
When I was younger I tried waist training but unfortunately, my skin is very senstive and couldn't handle it. To me, summer would not be the best time to do this, I would wait until fall only beucase in summer you sweat more and all that moisutre will be trapped under the corset all day which can lead to skin issues. Of course, this is just from my own experience, I'm sure lots of gals have waist trained in summertime with no problem! Good luck