Hi @Co_rUpt,
Okay, the HP web site's support pages have a service manual available for what I believe is your computer. The title there is "HP ENVY 15-cn1000 x360 Convertible PC", so I believe I have the right one.
Maintenance and Service Guide HP ENVY x360 Convertible PC
The Computer Components section lists the battery as part number L43267-005. A quick search using that part number shows the available on eBay, Amazon, Walmart and several other vendors. Newegg has a genuine HP battery with the correct part number for about $45 USD.
New Genuine OEM HP Battery 55.67WH L43267-005 Envy X360 15-DR 15-DS 15M-DR 15M-DS 15Z-DS 15T-DR 17-CG 17M-CG 17T-CG 15-dr1xxx 15m-ds0011dx 15m-dr0012dx Series L43248-541 HSTNN-OB1G SA04XL - Newegg.com
Unfortunately, it doesn't look like there's a guide for your computer here on iFixit, but the HP service guide in chapter 5, Removal and replacement procedures, has the instructions for replacing the battery starting on page 30. I read through it and to be honest it's one of the easiest battery replacements I've seen on a laptop, at least the ones where you have to take off the bottom cover to get to it.
If you can work a screwdriver you should be all set, but you're welcome to come back and ask questions if you run into any issues.
By the way, if indeed your battery has begun swelling, you'll want to replace it sooner rather than later, as in, NOW! iFixit has a Wiki page on the subject that's worth a read.
What to do with a swollen battery - iFixit