Do you want the reality? Oaths for all their lauded two way pledge and responsibility were more often then not a one way system empowering the higher party at the expense of lower party, especially when the lower party was a simple knight.
Or at the expense of the king if enough barons get together; it all depends on who does what and who is friends with who, but having oaths of service and oaths of this and that would still, in my opinion, be a nice roleplaying touch.
