My son is 8 months and loves his taggies blanket is it okay for him to self sooth and sleep with it in his cot? J

Red Nose recommends all babies sleep with their head & face uncovered.
https://rednose.org.au/article/what-do-the-safe-sleep-recommendations-mean

Soft toys/comforters are not recommended for babies less than 7 mths of age. (preferable up to 12 months age)
For those older than 7 mths, like your baby, it is important for parents/carers to weigh up the risks and benefits of providing a small soft toy to support infant settling.
https://rednose.org.au/article/soft-toys-and-comforters