Hello Alex,
I wished I knew what to say to help you... I was in a not so dissimilar place 30 years ago.
How am I ever going to find clothing or even shoes?
You are young, that's a plus. Sure you are big... you know what, when I was your age, I was the tallest person in my class, with the biggest shoe size. AND yes, it was a major factor why I never dealt with this back then. I went to a professional make-up artist to make me over and I ended up looking like a drag queen. It took me 10 years to fully dress again and that wasn't a very pleasant experience either. But my point is, now I am average height. I am less than 2 shoe sizes from being able to buy any shoe I like in a shoe shop. Young people today tower over me, both men and women. Each generation grows bigger. My daughter is 7 years old, she already wears clothes for 10 year olds, she is half a size from size 1 shoes... and she is average height in her class among the girls and one of the smallest shoe sizes.
You might feel big now, but trust me... in 20 years time, you will just be average. I don't have much in the way of clothing but I bought most of it off ebay.
What do I do about my parents?
Your family is homophobic/transphobic.... well mine are both of those things and racist, sexist, and every other form of hatred you can think of... my father is an active member of the far right. When he was younger, his pastimes included going gay bashing on a Saturday night before hitting the drink to celebrate. Guess what... he grew old. Went to punch me one day and I laid him out. Tried again and I put him back on his back again. It is really difficult, our family raise us, and show us love throughout our early years. Even when they are polar opposites of everything you believe in, you still love them. No matter how much contempt they show you, no matter how much violence, you can't help it. You know what I found when dealing with abusive people... don't let them get a rise from you. Smile and be polite... it infuriates them more. I argue with my Dad, I don't let him get away with it, but I present reasoned arguments without raising my voice and when he loses his rag, I just stand back and let him rage, he won't lift a finger against me anymore. I will be sad if my parents disowned me if/when they find out but it no longer bothers me... my biggest concern is my daughter.
How do I cope with dysphoria without transitioning for the time being
This is a tough one... you can do things to help but it won't go away and the more you delay dealing with it the more it is going to build up. The first thing, which I worked out this week... do not try to overcompensate maleness... that makes it much worse. My worst episodes have all been a year or two after trying to butch myself up. Allow yourself to explore your femininity behind closed doors, do not allow yourself to be ashamed of who you are. Ask your boyfriend to refer to you as she... that in itself is a buzz. Reason in your mind that gender is a social construct and that you are a person who isn't just defined by their gender (doesn't work forever but it helped me for 20 years). If you can set yourself some milestones so that you have something to look forward to... be realistic but don't leave it too long.
I've just started my journey, so I can only go from what I've read, but I hear a mild dosage of hormone treatment can help bring it under control - I am sure someone can confirm that or dismiss it as a myth.
Is there any general advice or even an anecdote you think would help me?
Try to overcome your fear and don't wait too long. There are people here who can help you. Keep the forum open or check in every day, so you don't feel that you are alone the world with this problem. There are no overnight fixes, one step at a time.