The other day DD had a great game banging spoons on the kitchen floor. The kitchen leads directly into where DH works - no door - we just can’t do that.
How much would a door cost?
What are the practical difficulties around fittiang one?
I take it from your comments about DH and the parcels, DH and your baby crying when you nip to the loo, DH and the wet towels, DH and the farting, that DH seems to be unable to concentrate on his work where he is. Fitting a door (plus perhaps soundproof panels) would help you both. I assume you will feel this is impossible though.
The fact that you can't appreciate suggestions of solutions and can't see any way of speaking to your H bespeak hopelessness. This comes across strongly.
I/we 'just can't' do anything to make this better... This is how my life will be, forever more, amen... I have lost the only time I could ever have enjoyed with the baby, and it will never be back again...I can't speak to DH about this without risking the entire relationship...
Essentially, you don't feel comfortable talking to your H about how you are feeling, and you have ruled out all practical solutions involving space that might make you feel better. Your own feelings are holding you back here. You are imprisoned to a large extent by your feelings of disappointment and loss and hopelessness. You are describing a strong sense of loss - loss of the mat leave you dreamed of, and loss of feeling you can be yourself in your own home. But there is anger too, and you need to get to the bottom of it.
The level of anger, the sarcasm, the snark, the division of posters into good camps and bad, directed at other human beings in your posts is not explained by constant questions about working in the bedroom, or the garden.
You say you are not interested in therapy, but you sound depressed and overwhelmed and lost. I urge you to consider talking to your GP. The feeling that everything is impossible and nothing can be done to make it better, even talking to your H, is an indication that you might need help.