I’ve only got one officer so I’m unable to complete anymore special operations. I’m level 8,..

Probably times are different now? As we reached the similar level though, we already had 4 officers by default. 1 during the tutorial phase, as you reach HQ level 5, you'll already be able to get Victoria and Bull -- which gives you 3. Lastly, when you defeat the first section/stage of the Special Operation or join the Counterattack, you'll earn Additional Officer/s; Doctor Comedian or Martin. By HQ level 10, you'll have 6 in total including "Starter Guide" which you'll get from your 7th day playing the game.