Hi Reallylovetherain,
I’m not sure I should be doing this considering your title said “narrowing” down your options rather than “broadening” your options but there are a number of very good threads in the forum about mattresses and children that include some good information and links to number of good choices that are available to you. They are linked in post #2 here.
As you probably know … a toddler needs a firmer mattress than an adult because of their less curvy body type and their need for good support and alignment while they are developing and if you choose a thinner mattress with durable materials then when they reach their pre-teens or teenage years and begin to mature and need more softness on top you can just add a good quality softer topper and extend the suitability and the life of the mattress.
Phoenix