Synology NAS (basically a hard drive always connected to the home network and internet) - has been amazing for auto-backing-up photos from the family phones and for running Plex run my own personal streaming service for the whole family around the world. Has been great for file transfer too. I can easily move files between my phone, PC, Steam Deck, etc and all the USB memory sticks I had have been sitting in a drawer ever since.
Exercise compression thermals - wear these is super comfortable and really warm. I wear them constantly at home and can have the heating off almost all winter (UK). Saves tons of energy and money.
Electric blanket - another great low energy purchase for relaxing under when watching TV or warming up the bed before sleeping. Gets super hot while hardly using any energy at all.
Split unit air con installation - this was expensive and I thought it would be unnecessary in the UK, but it seems to be used more and more every summer as we get more heatwaves and summers are becoming unbearable.
Safety razors - I have really thick facial hair and the multi-blade razors from big name brands would dull really quickly and cause tons of shaving rash. These razors are sharper, last longer, are recyclable and much better for my skin.
Liquid ink refillable rollerball pens - I tried fountain pens after seeing the online communities that are crazy about them, and really didn’t like them. I found rollerball pens I like that take fountain pen ink and have been super happy with them. I write a lot at work and this has gotten rid of the plastic waste of throwing away used disposable ballpoint refills every couple of weeks.
Hitbox controller - I’ve been playing Street Fighter 6 since release and I made a leverless controller box myself and I’ve loved using it to play SF6. Managed to make it for one third the price of what these things sell for and completely customised it.