"If either of us get some time at home alone it goes without saying that it is spent ironing/cleaning/vacuuming/washing"
I would set a timer and have both adults do an hour's intensive cleaning up, and then stop when the timer bleeps, otherwise it will eat into every moment you have. Any home can be dealt with in 4-6 hours a week, that's 2-3 hours each, and that should include your laundry and ironing. Seriously.
"I am 3 months in and really struggling - we both work full time, we have a 1-year-old and no family around. We don't have a cleaner or an ironer (and we have a LOT of ironing... "
I suggest that either you get a large tumble dryer, or you only iron things you wear in public, and avoid ironing bedding, table linens, pyjamas, and anything you can get away with just shaking out and hanging up. Also are you leaving it in the washing machine too long, or filling the washing machine too full? Those are both things that generate a lot of ironing. If you accidentally do this, it is better to halve the load and quickly re-wash it rather than struggling on.
"There is no supermarket nearby but online shopping takes just as long".
Set up a regular order and just eat the same stuff each week. Many online supermarkets have a facility to refill the basket with your regular items.
"We don't help ourselves either as we 'make' extra work for ourselves. If we are all at home on the weekend with no visitors (rare) then the spare time will be filled with something dull like doing the accounts".
That is family life 
"DH is a tradesman and will end up picking up jobs at the weekend if there is something going".
Fathers do that. It's called supporting the family.
"If our family visit they create work rather than helping us out".
Visit them instead?
"Our house is going to rack and ruin as is my body, our relationship is suffering, I for one am completely exhausted".
My darling, you need a holiday. Any chance of one?