If I agree to a salary sacrifice, won't other parts of my pay package be linked to a lower level of salary?

No.  Salary sacrifice earnings are used to calculate tax and NI contributions but any occupational benefits (life cover, overtime rates, bonuses, etc) will use a Reference Salary figure.  This is the salary level before your sacrifice so you will see no change in these benefits.

However, for state benefits which rely on actual earnings (e.g. state pension, maternity pay, etc.), the reduced figure will be used.