I don't see what's so difficult about having a shower every day. If that doesn't help, then carry on afterwards with some deodorant and perfume/body spray.
I always make myself smell nice and I hate those hot days where I know I stink. I often carry something round with me for such emergencies.
A friend of mine has a boyfriend who doesn't smell good at all. He has really awful body odour and you don't have to be stood too close to him to smell it.
I had them both in my car the other day and it was going straight up my nostrils. I had to keep sticking my head out the window because it was so horrible.
Anywho, I didn't feel like it was my place to say anything, but at the same time I don't feel confident enough to speak to my friend about it. I think it's better left unsaid. However, if it was someone close to me I'd probably have to find a way to tell them.
I have no issue telling my boyfriend he stinks on a hot day, but with anyone else it'd just be too awkward.