ESD protection for work with CPU/GPU
Quick answer is yes, you should always take into consideration ESD risks.

You should have an ESD protected surface and a ground strap (there is some argument for ESD protection gloves, but you don't see them in use much, at least I haven't seen them used much in industry).

The ground mat (like this one:  Maplin anti-static mat) is the most important bit (IMO) as you can us that to give yourself a good grounding to reduce your ESD. But you have to make sure the matt itself is grounded, that is the most important bit, any expense on ESD protection is wasted unless you have a good route to ground.

Many bits of ESD protection (such as the one linked to) have clips to attach to a "good ground", but you can also get plugs (like in this kit: Maplin anti-static kit) which would be my preferred option.

But I would say that re-balling a BGA is a very risky operation anyway, I would be more worried about that than the ESD risk.