Half-canvas construction makes a real difference: a canvas sewn in from the shoulders to mid-chest instead of an interlining glued to the cloth. Such a jacket gradually moulds to your body, breathes better than a fused one and does not stiffen after a few hours of wear. The Greg and Zico models, among others, are made this way.
For meetings that call for more formality, choose single-breasted jackets with a clear lapel line and a classic two-button front. Light colours work well in summer, for example the light grey Zico jacket in wool, with notch lapels, flap pockets and a cupro lining. Tomas trousers in the same shade are sold separately, and together they make a light suit for a client meeting. A double-breasted jacket can also work in summer if the cloth is light, although it looks more formal than a single-breasted one.
Colour matters a great deal in summer. Dark navy is still safe, but in full sun it can look heavy, especially with dark trousers. Lighter navy, mid and light greys, and beige where your company culture allows it, all work very well. The aim is not a holiday look but a fresh, daytime one.
Remember, too, that you take your jacket off more often in summer. Your shirt and trousers therefore have to look right without it.