At three months a baby is able to see things further away- so bright mobiles that move easily in any breeze are advocated for visual tracking and concentration.
Montessori mobiles are expensive, but you can make something that works just as well with a few feathers, light cotton and an embroidery hoop.
The great thing about this idea, is that you can re-use the embroidery hoop for a different mobile once this stage has ended.
Simply tie the feathers to a length of light cotton thread and then loop around an embroidery hoop. Attach hanging threads to the top to suspend from the ceiling.
It is a good idea to place the mobile near a breeze or open window so that the feathers turn slightly.