My sister-in-law is a bit taller than you at 5 ft and maybe an inch or two. She weighed about 105 and wore a size 5 when she had IVF. They implanted three embryos and two took. She carried her boy and girl to 36 weeks no problems. She had them naturally. With twins they tend to be smaller and then they are easier to deliver. Her twins were 3lbs 11oz and 4lb 3oz. She gave birth easily in a very short time.
My great grandmother was 4'9" and had her first baby at 14. She gave birth to 9 or so kids....two sets of twins. She was a twin herself. All of her children survived to adulthood except one.
I think you and your husband are little too concerned. With todays technology the doctors will monitor you so well the chance that anything goes wrong is slim to none.
I'm 40 years old having my third child. I had two miscarriages between the second and this one. Turns out I have a gene mutation that causes blood clots. I inject a blood thinner everyday, they do an ultrasound every month, I was monitored by a cardiologist for awhile for extra heart beats (they have been corrected with magnesium supplements) and my OB sees me a little more frequently than normal. They sent me in for two glucose tests because the first was borderline. They are so caustious for me. They monitor me so closely I feel perfectly sure that everything will be fine.
I am c-section because my first was very big and wouldn't come out. But even that isn't a big deal. I was up walking around the next day. And only took one Tylenol when I got home for pain.
You will be fine. Relax, enjoy, and anticipate the wonderful additions to your life.
PS I don't believe most insurance companies will pay for IVF if you don't do at least two embryos.