Separation Anxiety and Sleep (lack of!) 2 year old

My little boy (just 2) has always been very clingy since birth (Clingy to Mum and nobody else). He used to cling onto my clothes, check where I was in the house, need me within a metre next to him. This has gradually improved in the day. He still can't play alone for more than 5-10 minutes but is now accepting of his older siblings to play with him rather than just me (Mum). Dad does bath and puts him to bed every night (once he left our room at 9 months) so Dad could share some of the child care. I put him down for his naps daily. He goes to nursery twice a week for the day. At night he's so much worse. He'll eventually fall asleep (takes about an hour) but it's not terrible but then wakes at 12am, 1.30am, 3 or 4am sometimes 4.30 instead and then it's touch and go if he will go back to sleep. He did have a period of sleeping through for about 2 weeks and then that went. He wakes and needs us to resettle - have a hand on him and we've tried sleep training not to keep a hand, moving back little by little, trying to teach him to self settle but it's not improving. Any slight movement in the room and he sits up and knows and checks if we're there every 10-15 minutes even when he seems to be asleep. We both work stressful jobs and are desperate for some sleep. Even when we bring him into bed with us on occasions (very rarely) he needs to be touching or lying on top of me and have a hand on his back- as if he's petrified if I go. We tried Lycopodium, Belladona but no changes. Any help would be hugely appreciated. Thank you!