If you were going bespoke/custom/MTM you could have picked the cloth that fits the temperature range you mentioned. Anything in the 260-290 grams per meter will be fine.
If you want RTW suit then you will have to feel the cloth before buying.
As for the color, I think a plain Navy Blue suit with a white shirt and maroon/red tie with plain toe or cap toe black oxfords will work the best.
For the second wedding, try the same suit with a different shirt/tie combo.