We are not businessmen, we are not sales, we are just designers, sometimes play with ideas. Is a suit too stereotyped for us for interview? How do you think?
Don't overthink this. Dress for a job interview the way you would expect a consultant in your own field to dress for a sales call on a managing director / CEO. There's nothing wrong with being overdressed for an interview, but there's plenty wrong with being sloppily or distractingly dressed.
You can't go wrong with a business suit.
Your purpose in choosing clothing for an interview should be to allow you and the people you're meeting to focus on what's truly important to you and them. I suggest dressing as if you were making a sales call on their management because you are doing that. It's a small sign of respect.
You may run into a workplace like @Vietnhi Phuvan's where they're inclined to mistreat you if you're a little overdressed (see his comment below). You also may run into a workplace where everybody wears very expensive Armani suits. In either sort of place you may get a hard time for your ordinary but respectful department store clothing.
If you get a strong negative reaction to your clothing, be happy! You found out what's really important to the people in that workplace. That will help you make good employment choices.
(If you're an actor auditioning for a part, don't listen to me!)
You will be customer facing so you need to dress professionally. But as a designer you should show a bit of style. What you would not want to do is wear jeans like a developer might get away with.
For a man maybe a suit but one less structured than a typical business suit.
For a woman there are more options such as a silky dress with a jacket, a nice pant suit (but one that is stylish not stogy) or a less stuffy suit with a touch of color. What you would not want to do is be too sexy, show too much skin (and especially no showing your midriff), wear a very short skirt or clothes that are too tight. You would not want to wear super high heels (regular ones are fine, but keep them more business like rather than lets go out dancing.).
It is a bit of a fine line. You want to show some style to show that you are a creative person, but you don't want them to be afraid to put you in front of a client. The more conservative the industry you would support, the more conservatively they would expect a designer to dress as well.