It’s important to talk and understand what is part of “mental load” for the other. There are some aspects of life that you might not think is a load but is for your partner. I’d say that anything that would make you less tired will have a positive impact on your capacity to handle mental load as well.

• Go for a walk outside with the kid during its nap so the other can sleep (even a small noise from the baby could wake you up)
• The house will be less clean and tidy than before : how much does it have an impact on you (you tired + house is a mess)
• You can anticipate your medical appointements and check when are mandatory visits (check up + vaccines)
• Clothes will not last long, try to get some “old baby clothes” (they have been worn like twice) so you have always clean clothes + you don’t have to run to the shop because its too small
• Leave clean baby clothes in your trunk.
• You can subscribe to automatic diapers delivery online (+ wipes etc…) so are less likely to worry about running out of diapers