Its only 2 years old, though. how is the HDD already going bad? Also, any SSD's you'd recommend? The current HDD has a 2.5" form factor.
As dpareja said, electronics can just say "fuck you, I don't wanna" some times. Especially hard drives. The most likely components on a computer to fail are the hard drive, the disc drive (if your computer has one) and the fans. Luckily, these are also usually the easiest and cheapest components to replace. Even on a laptop.
If you do choose to change out the drive, two things: 1) you can get a Windows installer from Microsoft for free. You just load the files onto any 4gb or bigger USB 2.0 flashdrive (which you can literally get for under $5) and you've got what you need to reinstall Windows. It's actually a heck of a lot easier than it sounds. The hard part is getting your Windows key, which, if you're lucky, will be on a sticker on the bottom of the laptop. If you're not lucky, the good news is that you can use the full features of Windows, save changing your desktop background and having a watermark in the corner, for free, forever.
2) Brand is less important than capacity, so long as you're going for a reputable brand (I personally have a PNY 1311, for the record). I only have a 128gb SSD because I have two 1tb hard drives, as well. While swapping out my disc drive for a second drive is something I have been considering doing to my laptop for the last few years, most laptops, especially newer laptops without disc drives, don't have room for a second drive. The advent of the m.2 slot has only been an excuse for manufacturers to make their laptops thinner, instead of the higher utility of having an m.2 SSD boot drive and an HDD storage drive. As such, the size of SSD and, unfortunately, the price will be determined by your needs. I personally wouldn't go lower than 500gb if this is going to be your only drive, but others, like my parents for example, use a grand total of 200gb of their 1tb hard drive.
TL;DR: Look at how much space you're using on your current drive before you decide which SSD to buy.