Change Internal drive for a SSD in Macbook pro 2011

Hello to all, I have an early 2011 MD318 Macbook Pro (latin version). I would like to improve two things:

1. Change the actual internal disk (a regular 500gb 5400rpm disk) for a SSD one. Is this possible? if so, wich trade mark and specs should I search to buy a correct one?

2. Battery: mine is almost dead so which one should I buy?

Thanks in advance.

Barba