VivianChaste i have yet to see where to find one, but i do want a bra
You could start with a cheap Chinese bra to find out how it is wearing one. If you like it you can always look for a made to measure one from My-Steel for example. To make it even more secure you could have chains connecting the bra to the belt also. Then you will be quite sure it stays where it should be.
So it will be wise to have D-rings at the side of the belt and an extra D-ring in the crotch area for the thighbands. Then you can have a chain pulling your legs together when you will be sitting. Very lady like.
Rina Solo keyholding is kind of hard without using a timed lockbox, I'd recommend having a keyholder you can 100% trust, if possible.
A timed lockbox is better than nothing. But a real KH is much better. Remote KH is possible if you find someone you can trust. Trust is very important of course. You can also think of a combination of a timed lockbox and a KH in order to get to know each other and build trust. You can set a long time for the lockbox for example. And if you need to be unlocked before the box opens the KH can unlock. You can set a guaranteed maximum time then. If the trust builds you can increase the time for the lockbox.
There may be other options as well. Give up control and being completely at the mercy of your KH may be a next (big) step. If your KH says no it really is NO then. Then the experience will be very real.