"Dressing down" with sneakers and so on

Hi guys!

I know this is out of the ordinary – but I really want to be able to wear a suit without having the “stiff” look about me. And now that it’s summertime I’ve been looking at grey suits. I’ve been reading back and forth and from what I can tell, the best options for your feet are classic sneakers like Jack Purcells, Vans and the like. And I think that another way to take the heat off could be by wearing a t-shirt with a small v-neck.
But how can I make the whole outfit work? What colors are the best to opt for?
I was thinking grey suit, red sneakers with white accents, a white t-shirt and a red’ish pocket square – but that’s just after reading one article that I stumbled upon – I have no idea how that would work out for me.
I’m 6 feet 9 inches and slim of build, so the red accents might stand out a tad too much so maybe navy would be the better option?

I could really use some professional insight!