I'd urge you to seek counselling for this as you need to be 100% on any decision you make.
A few thoughts (I have an 8 year old and one more on the way). Divorced from child's father (very amicable now) and been with current partner for just under 2 years. Also renovating a house slowly when funds allow.
House - You can renovate with a baby, you can have work done in the house maybe after a month or so, but it can be done. No kitchen is a very temporary inconvenience, and would relying on family for a little while be so bad?
You can still have big parties, just one of you has to stay sober (take it in turns!)
You can still travel with a child, they cost nothing to fly with/don't count in the head count for numbers in hotels etc up to a certain age.
Your other half's son can still stay - and may want to be around more. It's his sibling, he might love the idea of it. GCSE's only take a few months to complete, a year with revision.
Finances are always a stretch, you can go back to work sooner (you only legally have to take off a small amount of time).
You can share maternity leave with your partner.
Have a plan in place a long time in advance for finances. Can you save more now and put some money away to cover mat leave?
Please don't worry about what anyone else thinks - it is none of their business. This decision should not be made based on worrying about what anyone else might (or might not) think.
You will still have support from your friends. You will also make new friends, those in the same/similar situation to you. Do you have family close? They will also offer support too. If one of your friends were to announce a pregnancy and you were no longer pregnant - how would you feel about this?
If you and your partner tried again and it were never to happen for you both - how would you feel about this?
You have time to make the decision that is right for you, but please do seek professional counselling, this is not an easy decision to make.
Good luck with your journey.