Underwear

I suspect that the combination of features you're looking for may not be available. Strapless bras tend not to be very supportive, unless they're the corset type with boning and lots of hooks!
I'd just wear a normal bra, in a colour to match the dress you're wearing. Straps showing are pretty normal these days- look at younger women.

I have worn M and S bras since I was 13 which is a very long time but no more the quality has gone. I am finding John Lewis better quality and wash well.

In this heat, why would you wear a bra? All that elastic and/or wires is so wretchedly uncomfortable and the heat just makes it worse.

Scribbles

In this heat, why would you wear a bra? All that elastic and/or wires is so wretchedly uncomfortable and the heat just makes it worse.

Because some of my dresses look better with my boobs "in place" than travelling southward. I'm lucky that they are still a reasonable shape and more or less where they need to be, but some of my lighter dresses really do look and fit better with a bra. The ones I've been wearing are ok, boned and "comfortable" but for some reason M&S have made them slightly shorter in the back so no longer fit but the next size up (40) is too big. It's not that the one I'm currently wearing has stretched with wear as it is only the second time I've worn this black one. If I can get away without a bra believe me I do, and as for showing the straps sorry but that's not a "look" for me. Was just hoping someone had actually found a reasonably comfortable, easy to get on strapless bra with some support 🫤

Ohh, I do agree about visible bra straps. Horrible! The sight makes me cringe. I have one ancient M&S multiway - at least 10 years old - which comes out on the rare occasion when I absolutely have to wear a bra and I lengthen the back with one of those little elastic Extenders which (I think) came via Amazon.

Try a sports bra or one that is stretchy and just pulls on over your head. Really comfortable.

Scribbles

In this heat, why would you wear a bra? All that elastic and/or wires is so wretchedly uncomfortable and the heat just makes it worse.

Why do you wear uncomfortable bras. I wear all kinds of bras but an uncomfortable one would only be worn once. Admittedly I am modestly endowed \9b cup), but I have no ida whether the one I am wearing has wires or not, unless I have a dig around to find out - no, it isn't.