You have a boyfriend who is so "porn star huge" that you, a petite submissive woman, cannot begin to satisfy him. The problem appears intractable given the experiences you describe. But here are two approaches you may try:

Fellatio: You cannot take more than half of his member without gagging. You ask about measures to expand your oral capacity. That is impossible. Instead, take him in his flaccid state. Take all of him orally just after he has come vaginally (see below). He will be especially pleased at how quickly he resumes. Many other women find this the only way to take an entire member.

Vaginal Sex: Here you will succeed. Persist in your search for larger dildos to gradually enlarge yourself. Keep in mind that your vagina is fully capable of expanding to a sufficient diameter to accommodate the head of a newborn baby! Look at some of the literature published on the subject of preparation for natural childbirth. You are on the right track.

Hopefully this advice will also be useful for other women facing similar difficulty.