Yaris came with 15" wheels with a 16" option offered on some models. You obviously have 16" option.
If you have stock (OEM) steel wheels with plastic covers, and you're broke it's a no brainer. Get your sexy little butt down to your nearest wrecker and pick up a pre-loved Yaris rim for $20. Nobody wants those things so don't be persuaded into paying $150 or something stupid. If you're lucky it may come with a good tyre too.
If you have alloy wheels, the relevant dimensions will be stamped or cast into the wheel, usually near the rim but sometimes on the back. It'll say something like 6x16JJ +51 or 6Jx16ET51
6 is the nominal width of the rim in inches
16 is diameter of the rim in inches
+51 or ET51 is the offset of the rim in mm - how far the rim/hub mounting face sticks in or out of the wheel arch relative to the centreline of the rim. All front wheel drive cars like yours have positive offset (written as + or ET) where the rim centreline is closer to the car than the hub.
J or JJ refers to the rim cross sectional profile. It states that the shape of the rim where the tyre bead sits complies with some Japanese automotive industry spec from way back.
Don't worry about it. Like VHS video format, JJ took over the world, and virtually all rims made in the last ~60 years are J/JJ compliant.
Your new rim doesn't have to be from a Yaris as long as the centre bore, PCD and offset are the same as yours. The Yaris has a hub centre bore of 54.1mm. If the centre bore of the new rim is bigger you may be able to buy spigot rings to reduce it, but it's a lot easier to find the right wheel to start with. Your PCD is 4x100 (4 mounting bolts/holes arranged on a 100mm diameter). Very common.
The 16" Yaris has +51 offset as standard. If your "new" rim is just going to be a spare to get you home in an emergency, then other offsets may also fit from +30 and up, but you'd need to check clearance to your bodywork as the tyre will effectively stick out more and may rub. Far simpler if you get the same size.