Here is an illustration of the 52.5cm (smallest standard size) Stanforth Conway. This measurement refers to the effective seat tube length, the actual seat tube length is 43.1cm.
For a height of 5' 3" we have estimated an inside leg measurement of 724mm (28.5") and a saddle height of 639mm. Based on these estimates the standover height of the bike is circa 0.5cm higher than your inside leg measurement so with shoes the top tube will be at a similar height to the top of your inside leg when the bike is 100% vertical. If desired we can tweak the angle of the top tube to give slightly more standover clearance.
It will be worthwhile measuring your inside leg measurement - if it's longer than 28.5" than it's likely the saddle will need to be higher than that shown in the image. To do this 1. Get a book and stand with your back against the wall, 2. Place the book in between your legs as high as it will go, 3. Move away from the wall keeping the book against the wall and finally, 4. measure from the top of the book to the floor. It will also be useful to measure the saddle height (bottom bracket centre to the top of the saddle) on your current bike and compare it against the illustrations.
If you would like a specific illustration showing your current saddle height or based on your inside leg measurement, then click here to send us your measurements in mm and the frame size(s) you are interested in and we will create it and email it to you.