ok if that shower is for kids then it's a fine size. I think you have JUST enough room for the freestanding bath.
I think you really want us to say yes, so YES!
I think I'd rather a 1200 x 900 shower if you can wriggle anything around. 900 x 900 is really small and I know it was the standard but not I'm seeing larger showers as more common.
Is this the only bathroom in the house?
The tapware can also be expensive too as you rise it from the ground or extra length from the wall.
I'm having a freestanding in my PPOR but it's going to be my PPOR forever