I also think a loan system would be good especially for players coming through the academy, they could be loaned out to teams in a lower division, thus gaining experience and progressing while not weakening the main squad. The teams could at the end of the season agree a transfer fee set by the parent club or the player reverts back to the parent club.

This could be run with another level of transfers, with a nominal 1 or 2 token cost and a small initial fee for the player.