If you insist on wearing a bra to bed then a soft sports bra is certainly better.
However, I'm a 34E and I cope just fine with no bra. Your breasts don't *need* a bra. They are actually meant to move around. I can totally understand wearing a bra during the day- I wear one during the day too, but not at night.
They don't *need* that support, they have tendons and ligaments that are there to support your breasts. The less you use your breast ligaments the weaker they become... so yes, if you wear a bra too often your breasts will sag faster.
EDIT: Also, there IS proof that wearing a bra too much causes swelling of the lymph-nodes in the breasts and causes build ups of oestrogen... these cause swellings and small cysts and the cysts *can* cause cancer... so yes, wearing a bra too much can, inadvertently, cause cancer.
If we actually *needed* a bra, we'd be born wearing one. Remember in the Victorian era when we women were told we were too delicate to sit up without a corset... so we wore corsets all the time and in the end we couldn't sit up with out a corset?
Same thing with bras.