I'd like to say a couple of things about this.
First of all, my sympathies on the loss of your baby. It's something I have never and hope never to experience.
Secondly, I think that the natural response to any sort of loss is to replace whatever was lost. I think that considering that your first pregnancy was not planned for, perhaps you are simply reacting to the loss? If you had not become pregnant to begin with, would you still be considering this? You had a baby growing inside, and now you most likely will need some time to come to terms with that.
I have never been an advocate of waiting for the perfect time, because it will never come. But there are certainly some times that are worse than others.
If your boyfriend isn't sure, you should wait. It will be his baby too, and his responsibility, and he could become overwhelmed with it. The fact that he wanted to wait is a good indication.
A baby is added stress, if your relationship already has some problems, you should work those out first.
And I want you to be sure that you realize realistically the implications of a baby.
I have a few questions you may want to ask yourself if you are seriously considering.
Can you handle going on as little as 4, 3, or 2 hours of sleep per night? For how long? Can you manage it for a week? For a month? Longer?
Will you be able to work, and if not, who will support you?
Do you plan to further your education? If so, how will you handle childcare?
When you envision having a baby, what is your reasoning for it? Is it because you want a baby to love and love you, or is it because you think that you can create and maintain an environment that would be beneficial to a child? Essentially, are you thinking of your childs best interest or your own?
I mean none of this to discourage you. I only want you to make an informed decision. I am the mother of a 1 year old little boy, i'm a college student, and wife. I wouldn't trade it for anything, but it is difficult. Sometimes i'm kept up until 2 or 3 am with my son, and then have to get up for school at 6 am. Sometimes money is extremely tight. Sometimes, even though I have a great relationship with my husband, we are both so stressed that we just can't get along. You have a lifetime to look forward to work and stress and responsibility, maybe you should appreciate your youth a little longer.
Or, maybe you really are ready. If you think you're up to the challenge, kudos. Whatever you decide, (of course, in the end, only you and your boyfriend can decide), I hope it works well for you.