Upgrading laptop

[FF04]

Hi, I have a Lenovo Legion y530 15ICH (i5-8300H; GTX1050; 128GB SSD + 1TB HDD; 8GB RAM), that completely froze a couple weeks ago. I sent it to the store believing that it was still in warranty. Apparently, it isn't, so they called saying that the SSD is dead and that the price to replace it is 400€. Of course I said no because the price is completely ridiculous and I've seen enough of Linus to know how to upgrade an SSD (even tough it will be my first time doing it). So I'm looking for an SSD of 256 or 512GB that can replace the stock one I have, my problem is that I'm not sure wich one should I get. Can someone reccomend me one that isn't overkill for the rest of the specs and doesn't bottleneck the laptop at the same time? I'm also thinking of upgrading the RAM, so any reccomendations of 2x8GB sticks would also be nice. Thank you :)