Hi Jnelson,
It sounds like you made a great choice (and it’s good to see that you changed from a plush to a firmer mattress). Congratulations on your new mattress 
If your child isn’t potty trained then one of the more waterproof or highly water resistant choices would be more appropriate. The thinner membrane types would be a good choice but they can degrade with washing and drying and sometimes fail so the protectors that use wool with a membrane (such as the NaturaProtect, the Glideaway Comfort Premier Mattress Protector, or the MyProtector from Sleep & Beyond would add an extra layer of protection and would help more with temperature regulation.
Once of the wool puddle pads could also be a good choice (either with a cotton protector on top of it or just under the sheets) although I would check with the retailer you are buying from to make sure they are “water resistant” enough for a child that can have an accident. They would be more breathable than a protector that has a membrane but they can also be more more costly … especially if you use a cotton protector on top of it…
I don’t have any specific recommendations no but there are some general guidelines and information for pillows in the pillow topic here (although these are more about choosing a pillow for an adult … the same principles apply).
There is also a good article here about pillows for toddlers and I would make sure that if your daughter needs a pillow at all that it is thin enough for a child and isn’t an adult pillow which would be too thick and put her head and neck out of alignment. A pillow that has adjustable filling (such as one of the shredded latex pillows with a zip cover that allows you to reduce the fill material) could also make a good choice so you can customize the height of the pillow to match your daughters needs.
Phoenix