It really depends on what you mean by unable to afford it. Have you worked out a proper budget? Having done that, could you afford to have a child where you use reusable nappies, second hand clothes/hand-me-downs, no foreign holidays, healthy food etc. If you can provide basic needs, then I would go for it within the next couple of years. At 30 you have time, but you don't know if you'll hit fertility problems.
I grew up in 'poverty' as defined by the government. However, I do not actually think this was poverty. My parents managed money well, fed us healthy, cheap, home-cooked food, and we always had shoes and clothes. Heating in the house was scarce, and we relied on extra layers and hot water bottles, but were never too cold. We got a sweet treat once a week. We got hand-me-down clothes and sometimes second hand shop stuff. We never had games consoles etc. We had board games and outdoor toys like balls and hula hoops. We went on walking and camping holidays in the UK, or stayed with relatives etc.
I had an amazing childhood despite being in 'poverty', and I defy anyone who says 'I wouldn't raise a child in poverty' to tell me that I would have been better off if my parents had decided not to have me at all.
Money management is crucial, and many people wouldn't have the discipline to manage on so little. If you and your partner do, and you don't want to risk not being able to have kids, go for it.
On the flip side, if you can make say a two year plan, with a realistic chance of increasing income or decreasing mortgage costs, maybe do that first. It would make life easier to have just a bit of spare cash.