I, too, briefly floated the idea of a 3rd, but practically so much changes with a 3rd (and it's much more than the jump from 3 to 4).
Firstly, cars often need changing/upgrading. Secondly, sleeping arrangements (now, and in the future) need reassessing.
We often joke that two's enough - one for each hand. But now ours are in their early 20s, we have no regrets. Both financed through university, no change of car or house/sleeping arrangements when they were small. We have friends with who 'went for' a 3rd, and also friends who 'rounded up' to 4.
Without a doubt (ok, ages have a part to play, but can only go from our friends) that the one with 4 felt it made life, whilst not exactly easier (far from it!) but more 'even'. 3 is hard an odd number both in maths, and in families... but again, I must stress that I can only go from our friends' experiences! Many families find 3 is their perfect number!
We also experienced a MC at 13 weeks in between our two, and often wonder what life would have been like without DC2 that we do have, but I feel our decision to stop at 2 would have been the same.
Only you and your partner/husband can decide if it's right for you. It's a cliche, but children are for life - and not just to the age of 18. LIfe doesn't always legislate for the unexpected, so sometimes you have to compromise in the short term for the long term good.