I do meal planning but then build an element of flexibility into it, e.g. by having a few vegetables that could be used in either: stir fry (with cashew nutes / frozen prawns), pasta with cheese/tomato sauce, risotto, thai curry, etc etc. This works well for us. I alternate between quick meals (above) and longer to cook meals that I do when I get home from work early enough.
Key rules for me -
Don't overbuy perishables (better to top up in the week if necessary)
In contrast, also have in the longlife basics for things you cook a lot (e.g. tinned tomatoes, garlic, onion and tomato puree to make a tomato sauce)
Learn a few basic sauces/recipes so you don't need to buy packets/prepared food
Vary the meals you cook a lot (e.g. Thai chicken curry works well with spinach / green beans /sweet potato - vary it every time) so it doesn't feel too repetitive
Anything that is an effort/timeconsuming to make should be for a second meal as well (not necessarily consecutive days - most meals are fine after 2 days and we don't mind that)
Don't know if that helps but it works for me!
I should mention I am pg with first baby, so no idea how this will pan out with a little one!