15 month reliant on me to sleep

[Starosaur]

My 15 month old's sleep has become terrible. He has never been the best sleeper but got a lot better at 12 months and would sleep through or just have one wake up. He normally fed to sleep for naps but would go in cot awake but sleepy at night and self settle. We went on holiday about 6 weeks ago which messed with his routine (new environment etc.), then once returning he had had 2 colds in a row and been teething - sleep has become a battle and I am rocking or nursing to sleep. He is waking 2-3 times a night. Sometimes when he wakes I feed and he drops straight back off, other times he doesn't and I have to walk/hold/rock until he eventually goes to sleep. I also want to stop breastfeeding and was down to morning night and before nap but now it's all through the night and don't know where to start to wean him off. He is a thumb sucker and has a muslim but does not seem to self settle anymore and crys, sometimes hysterical, when put in cot but will stop once picked up. He has just started walking so could this be connected? I'm a SAHM so we don't have a strict routine, normally wakes 7ish but sometimes earlier/later and bed 7-8pm depending on how naps have gone. He has recently moved to one nap a day if waking later, normally 11am for 1 1/2 or up to 2 1/2 hrs but if he he is tired and goes down earlier or nap is shorter will have a second nap mid afternoon. I know he has become reliant on me for sleep but how to I break the habit without meltdowns? Thanks for reading and sorry post is so long, any suggestions where to start appreciatiated