Mattress advice for big lad

Hello, I would like some advice on what sort of mattress to purchase.

I am around 79kg and 6foot, athletic build and exercise often.

My bed is king size and it it is just me in it.

I often find myself waking up and rolling over to another position as i think my current mattress is too firm.

I also tend to get very hot at night and often wake up with dead arms from lying on them (not sure if this has anything to do with the mattress).

My budget would be a maximum 350 but preferably less if possible.

Thanks in advance, Will >