I just had to post, though I don't really feel I can offer any advice - I am going through something very similar.
We have two sons, aged 5 and 3. I fell pregnant, still at a loss as to how, as we were using contraception, and spent much of the pregnancy worrying about how we would cope with three (we really can't afford it, live in a small two-bed, with a small car, no position to upgrade anything) But also got so excited as deep down I think we both always wanted trhee, and decided that we would just deal with things somehow.
Anyway, I lost the baby at 11 weeks, and like you, am feeling so conflicted. I don't have to worry about the practical difficulties of dealing with another child, BUT I feel so empty.
I had another miscarriage a few years back, and the way I got over that was to focus on getting pregnant again, and I feel I don't even have that to focus on now, just the sadness.
Neither my husband nor me feel brave enough to say, to heck with it, let's just have anohter, we really would struggle.
I also feel really sad that my reproductive years are ending on such a low, somehow this last miscarriage is overshadowing the wonderful births I've had and leaves me feeling like I've failed somehow.
So, don't know what to say to ease your sadness. Hopefully with time we'll be able to look at it more rationally, just accept that for now there is going to be this deep sense of loss. Sorry for not being able to say anything more positive, but sometimes it helps to know that others are grappling with the same...