baby bath seats

Hi,My gorgeous son is coming up to 10 months and as much as he loves the water and his baths, it's proving a mission to bath him as he wants to stand up or move around whilst bathing him. As much fun as we have I was wondering if anyone out there has any ideas on which is the best bath seat to get and if there is any point at this stage as I'm also using a bath matt in a baby bath but he is getting bigger and bigger by the day and will soon be in the big bath but I'm a bit apprehensive when that will happen that he will not stay in one place!
Any advice very welcome.
thanks
Carole