I went back to work at 6 months, I pumped in the day so baby got breastmilk bottles while i was out and I breastfed at home.
He was totally fine in the day. Seemed very happy.
But the second I walked through the door, he was superglued to me. He would breastfeed for 30 minutes +. My DH had to peel him off me finger by finger just so i could eat dinner or go to the bathroom.
He also started reverse cycling, eating less and less in the day, and waking at night to eat massive amounts of milk every 2 hours.
By 7 months, I was getting less sleep than the newborn days AND working full time.
It was hell for a few months but by 9 months he was on 3 meals a day so i could stop pumping in the day. As his food intake went higher, his neediness came down.
So really the hard part is for a very short time.
If you don't want to breastfeed anymore, then I think you should move to formula now, don't make all the changes when you go back to work.
I am happy I persevered with breastfeeding as it's very useful now at 14 months. Helps a lot with teething, overstimulation, general connection, it relaxes him and soothes him and it's really quite lovely. Great for travel too (we flew long haul at 12 months).