Pros:
I really want one and think I would regret if I don't.
DP would be thrilled if we have another
DS wouldn't be an only child and would have a blood relative once DP and I are gone.
Cons:
I'm 37 so a pregnancy would be high risk.
DP is on medication which could damage a foetus so would require abstinence/flush out prior to conceiving. This would mean him suffering with pain and his condition potentially worsening.
I'm on ADs and would want to come off them before conceiving.
Our home isn't big enough for another child but we have no options for moving at the moment.
DS would prefer a dog 
Additional info:
Our relationship isn't great, more friendship than romantic, but we do love each other.
I had a miscarriage when DS (12) was a year old and it put me off trying again. A few years later DP was diagnosed with arthritis and was then retired from his job. We now live on his pension. In order to better our financial/home situation I need to go back to work.
I'm, to be perfectly honest, a bit scared of being tied up with another child until I'm about 60. I know I could cope with a newborn now, but it frightens me to think I might resent having a teenager when I'm in my 50's.
I keep on hearing people say you only regret what you DON'T do and I'm scared that time is running out.
What would you do if you were me?