The unltimate transom window has an arch. They are beautiful but very pricey.
If you don't have transom windows, rather than remodel (which has VERY expensive labor costs due to existing framing and supports) a less expensive option is to trick the eye. You can create the illusion of taller windows by adding window valances (see before and after).
Valances create the illusion of having transom windows & make windows feel taller.
AFTER above BEFORE below
Whether or not you should add transom windows depends on the following:
1) your budget, they can add a great deal of expense
2) will it distort the exterior view? For example, you could perhaps add a transom in the center, as long as the exterior view would still be symetrical
3) when a covered porch limits how much light is coming in.
4) If it's even possible, example, we often cannot add them due to the support (wood framing) above the window. In that case, you may be able to add windows on each SIDE of your french door instead.
The Eclipse transom window below is far more expensive than a straight transom.
It creates a more traditional look.
This transom window is the focal point of the room
Whether you can add transom windows will depend on your current support beam needs. Often it depends if there is a 2nd floor above the space. The arched shape is a more traditional look, a straight transom often looks more contemporary.