As specialmom said, rather than a tubal ligation, practice another form of birth control. Also, speak with your OB/GYN regarding everything.... your over all health, the pregnancies, etc. and perhaps he/she might have a recommendation. I understand and appreciate your concerns regarding your husbands wishes, but if your doc suggests a procedure, I'd say you take that seriously. Your health is of the most importance, and without that you are no good to your husband or children/child.
Not that I'd do something my husband and I didn't agree 100% on...but who says you can't do something without his consent???? It's your body and if you want to do you can. You don't need someones permission.
Now having said that, you've been pregnant for 4 years. You deserve and need a rest. If he argues with you, tell him he can be pregnant for 4 years. Pregnancy is not an easy thing and is very taxing on the body. After this baby take a break. Let your body heal and rest. It needs it.
I'm sorry about your miscarriages. Were they after your son so you've had them in a short time frame?? That really does something to us hormonally and emotionally! So, I'm sorry about that.
I think that in all honesty, I would not do something like a tubal without my husband wanting me to. Doesn't mean you have to have another baby----------- practice birth control!
Anyway, you haven't talked to your husband yet----------- so do so. Maybe he'll think it is a good idea as well. Then do it if you feel you want to. But if he does not, I'd just use birth control faithfully (IUD is an option that is more longterm).
good luck and happy baby!! Oh, and I wouldn't make any major decisions right away until your mind has cleared and you are sure of it! Peace.