OP you’re doing brilliantly. Lots of people are stressed, a bit self absorbed, having problems in their own lives & judging others makes them feel better about themselves, temporarily. Ignore/pity them.
If you’re near an ikea they often have model tiny flats which enable you to really visualise imaginative storage ideas.
I really like the Japanese tradition of roll up futon mattresses that go in cupboards by day. Also agree the Hemnes ikea day bed with firm mattress is v comfy and works as a double too. A friend of mine put a double hammock into a bedroom to free up floor space - she used special fixings so it was safe to sleep in. Less expertly fixed ones - even made of sheets/whatever you have - would hold cuddly toys, clothes.
And as you declutter, remember everything you own is renting space from you which you might prefer to keep as space. So don’t be afraid to simplify eg what meals you cook - and so what equipment you need, what clothes you wear (everyone in darker colours and judicial sponging of dinner medals saves on laundry too) - it can be v hard to know what you may need/want in future so if you do have a friend who might be able store your posh dress for weddings & your champagne glasses for you, do ask. Some people have loft space for a couple of boxes.
3 is a hugely challenging age/stage! You know that it passes and this is likely your hardest point.
Meditation might help - there are free ones on YouTube.
And, this might sound ridiculous, but VR headsets are v cool - probably not worth buying for yourself unless you’re a gamer but if you ever treat your eldest to one, have a go, some of the games have amazing graphics and are set in nature and it feels like you’re really looking at a horizon. I loved using my son’s during lockdown, we were on the ground floor and v overlooked and it felt like a View. One for when the twins are asleep!
We are in WhatsApp groups with local friends and friends of friends where we share/swap games, big toys, DIY tools etc. it is v informal and works well: we check if anyone has an X they can lend us before renting or buying that item. It saves money, storage, is greener, and with games/toys is exciting to have ‘new’ stuff. Libraries of Things/toy libraries are getting more popular and tool rental for DIY often means you get a more powerful/efficient tool than you’d buy, and you needn’t store it. Anything you do buy like that, sell on asap.
I’ve no more ideas but wishing you huge good luck and lots of good times with your boys x