OP, some of the replies here are mad. I appreciate you are asking people for their opinion, but they are presenting so many 'what ifs?'.
The reality is that with any choice in life, we have no certainty of it working out well, or otherwise.
Of course you have to make practical provision for your children, so start there - but after that, it comes down to what you and your DH want, and I don't think any comments here will help with that.
Naturally, each of us approaches this with our own perspective and preferences, but ultimately it's about what you feel about family life, what feels right to you. You are certainly not a bad position to have another baby, but only you can weigh up the financial implications, the age gap, and any impact on career.
Speaking about having a preference, in my own case, I always wanted 4 children, had 3 in quick succession - my marriage was abusive, so clearly things were far from ideal, it ended when the smallest was a baby. I recognise that practically having 4 would have been incredibly hard - it's very tough parenting alone with 3 as it is - but I still miss that 4th child I planned to have, as illogical as that is. (my youngest is 14 now!)