We have the shunggle baby bath I got it in smyths for like £20 it’s so much easier, my baby also can’t sit up alone yet but I just watch her in it and she’s always fine as it’s on a slight decline anyway
This is the one we use https://www.smythstoys.com/uk/en-gb/baby/baby-essentials/bathing-changing-and-potty-training/baby-baths/ity-by-ingenuity-easy-rinse-baby-bath-seat-birth/p/223382
Our LB is 17 weeks and is 11lb6 and we have always used the angelcare bathseat but we put a cellular blanket down to make it a bit more comfy