You only need what you already have and weld "slightly" the spring in one place (no seat post / brace needed at first).
Support the front end of the boom on something up from the ground so i't about parallel to it.
Now put your foot on the boom and see how much it moves.
If too much, put a harder spring.
If too little, try to push it harder or sit on top of it to see what happens.
IF you're on top and it moved little, put a softer spring.
The idea is to see what happens with regular loads, ie. your body weight.

Regarding working space, i feel ya'.
If it makes you feel better, i currently don't have absolutely any workspace ...
I used to have a remote one where i could do some stuff but it's pretty much gone ...
I'll have to wait until after i've built the house ... and that's gonna take some time ...
On the upside, maybe it's sunny outside at your place. You might like that