Needing direction for starting sleep training!

Hello everyone! I’m ready to start sleep training and I’m just not sure what direction to go. Looking for any and all advice!

My girl will be 9 months at the end of this month. She went from sleeping great to taking a lot of time to be put down. We’ve (parents) coslept from day one as she would not sleep any other way and is still like this other than the rare occasion where she will sleep on her own until she realizes there isn’t someone next to her. I (mom) have contact napped with her for every single nap and she sleeps between her dad and I every single night.

Her schedule was wake 7-8am, nap 11a-12:30/1p, nap 3-5p, bed by 9-9:30pm. Now it’s wake up at 8:30am, nap at 12pm-2pm, nap 5pm, bed by 8:30/9pm and she’ll sleep until 10:30 and be up again until 12:30am-1:30am. I’m exhausted!

I’ll be going back to work soon and want to get her back to bed and/or sleeping on her own at a reasonable hour. We need all the help we can get.