MVHR design

We have a ventilation issue with our house, old 20s build with single block, chimneys and wall vents have been blocked up and insulation in the suspended floor. Considering single point d-MEV in the top stairwell but not sure it will do the job as we regularly have 80% humdity in some rooms.
Perhaps its better we should just go all out with MVHR either single units in most rooms or perhaps ducted throughout.
A lot of mvhr installation seems to be the ductwork so i was thinking DIY this part (upper flooring is all being refurbished by me anyway so can access the ceilings). then just get an electrician in for the wiring it up in the loft
Is this something you could help design with? what would you charge?
House plan attached.
Cheers