What are some recommendations for ED Visa processing companies in Thailand?

AFAIK; there are NO private language schools that can get a 90 day Non-ED visa issued inside the country at the immigration office. All the paperwork from the Ministry of Education and from the school is addressed to a thai consulate not the immigration office.

It pretty much works like this; you enroll in a school, pay the tuition and they get the paperwork from the MOE so you can go out of the country and get a 90 day single entry ED visa from a thai consulate. Then every 90 days they will give you more paperwork to take to the immigration office and apply for a 90 day extension. You do that for the whole year

Only Universities can do.

Your school is the best option.