Firstly, you don't need a reason to terminate a pregnancy. The only thing that matters is that you feel that you don't want to have another child, either at the moment or ever. No one ever needs to have solid reasons for you.
As a pure outsider, reading what you have written you don't enormously sound convinced. You see problems and difficulties ahead, but not disaster. (Not that I mean that in any way to suggest that you shouldn't have a termination if you want). That is, as littlered says, a very tricky position to be in. But you have time on your hands, by the sounds of it.
If you can, try and stop and imagine what the future will look like in both situations - having a baby, and not having a baby. Picture one, two, five years time. Is there a future you feel more comfortable with? Is there a future which worries or scares you?
Keep talking to your DP. It helps if you can come to a mutual decision, just in terms of supporting each other. Remember, deciding not to have this baby now doesn't automatically mean you are deciding not have children together in the future.
Many, many women will have a termination in your position - the feeling of not being ready to have another young child at that time, the worry of work and your financial future etc, the worry of what it will do to the family you already have.
Equally, work is just work, and if you have been re-establishing yourself now after returning to work after children, then you will be able to do it again in a few years. And an age gap of 4-5 years between your youngest will easier than an age gap of 2 years between your children.
Good luck, and 
. Keep talking if you want to.