If i were you I would just try some sort of lubricating cream or ointment when riding instead of changing from saddle to saddle. A cream will definitely reduce chafing and friction. You said you were experiencing chafing.
I believe urinary tract infections are caused by bacteria getting into the urethra, and I find it odd to say that an ointment in the general area would cause such infections. Good diet, keeping the urethra area clean and peeing regularly is the usual advice to prevent urinary infections.