With a suit, a lot depends on fit. Unless you are a very standard size in all proportions, know what you are looking for, and work with a retailer that you trust, I'd be wary of buying off the self. There are also only a limited set of alterations that can be done to most jackets.
If you are going to wear a suit, it will look and feel better if it is made to measure.
There are a few companies that do it online now, and I've had good experience with
IndochinoThe general business model is that you upload your measurements online, the suit gets made to your measurements somewhere in Asia where tailoring is dirt cheap, and then you get a "custom made" suit shipped to you.
The tricky part is getting the measurements right, the sites usually have guides and videos that help you do it. It is helpful to have someone else who somewhat knows and cares about suits to help you with that part. My wife (fiancee at the time) helped me the first time I ordered an Indochino suit.
You probably want to stick with a basic navy suit, or maybe a grey suit. Avoid anything fancy, and avoid a black suit unless you have reason to think that works for you. Check the Indochino "essentials" collection. Don't get fooled by the fancy stories on the other stuff. You just want an essential piece.
A navy suit is the most basic and versatile thing you can probably get. They work together as a suit for interviews, presentations, weddings, funerals, etc. You can wear the pants alone as a pair of dress slacks if you want, and the jacket by itself can be used as a sports coat if that's your style (great on a date when you want to dress up a little, but still be casual).
Good luck