Something like this.
It's just a lot easier to stop and start without having to swing your leg over the top every time!

Hi all,
I'm planning my first bike trip, across Europe and Asia, and I'm trying to design a frame bag that fits a ladies' bicycle. It will also convert into a backpack (My philosophy here is to make sure that every item I take has at least one other use - minimising weight by maximising utility. So far my kit weighs around 5kg excluding food/water). It will be the only luggage I take, besides a small security belt for my passport, wallet, and keys, and maybe a packable handlebar bag for consumable items.
However, I haven't yet come across any designs that work for the low frame of a ladies' bicycle; only for typical wedge shaped frames. The obvious issue is that it would probably interfere with pedaling if it spans the whole frame, but if I leave space for that, it may be too small or bulky.
Because I am still searching for a suitable bicycle, and in case it outlives the bicycle, I want it to be fully adjustable for any bike.
Can you suggest any improvements or flaws?
Here is my design so far:

A bit more of an explanation:
With the zip along the outer edge closed, it will create one fully enclosed U-shaped area. This area is divided by the two pockets on hanging down on the inside, but is open underneath them. In between those two pockets is another space that remains open on the outside. I could possibly zip this area up too, to create another separate section, but might be difficult to sew.
The straps that go under the upper tube, when used as a backpack, could slot something like a small tent or jumper on the top of the backpack.
The bottom of the straps are adjustable, like normal backpack straps, and can be used to go under the lower tube and tightened for extra security.
There will be a loop that secures the bag to the handlebar tube which stops it from slipping down, and this can be used as a handle to carry the bag.
The bag can be folded in half and zipped up, still hanging from the upper tube, but so the pockets are hidden from view from passersby. The zip wouldn't be fully up since the tube would be in the way.

Apologies for the poorly laid out post, still haven't gotten the hang of inserting pictures properly.
Thanks guys, and happy cycling!