You have multiple options in my opinion.
- See if your shop offers this Laptop with a SSD.
This would be the easiest option for you probably
- Get a M.2 SSD - your laptop supports the new M.2 SSD's which are even faster than the regular SSD's. If a normal user really needs this is questionable but having the option is nice. It is more expensive though.
If you want to get a M.2 SSD you can get it here. Any of these should work - pick one which suits your budget and read some reviews when you have doubts.
You would have to add this to your laptop yourself but there are some How-To's on Youtube.
I have made some good experiences with the Crucial and Intel SSD's - they were reliable and deliver a great performance.
EDIT:
Your Laptop supports M.2 SSD's with a formfactor of 22x80mm.
Source: Manual for this Laptop
But your manual does not say which M.2 Key Port it features - there are 2 different ones. 
Source: Kingston SM2280S3 120GB M.2 SATA SSD Review on legitreview.com
Your best bet when buying a M.2 SSD is to buy one with a B&M Connector. These will fit the M.2 Port always. So your best bet would be this Intel 535 M.2 SSD 240 GB from Intel for example: 
This will fit your laptops M.2 SSD port :)
Source: Intel ARK Page of this article
If you want to buy a SSD from another company then make sure to get one with B&M key connector and with a formfactor of 22x80mm.
- Get a regular SSD. Your Laptop has a built-in DVD-drive - if you are not intending to use it that much you could swap it out and replace it with a SSD. If you plan on doing that you would have to get yourself a SSD and a SSD/HDD Cage. Then you would have to replace your HDD-drive with this cage which houses your SSD.
So it depends on which road you want to take. You can't go really wrong with many of these. My Suggestion would be a Intel 535 M.2 SSD. But if you want to replace your DVD-Drive with a SSD then I'd probably go for the Crucial MX200 or BX100
I hope that this helps you a bit - if you still can't decide which one to buy or which path to take then feel free to leave a comment. I'll try to update the answer accordingly :)
