Products and services I recommend you buy and use
Inspired by the many, many others of these (e.g. Mr Bowman). No referral links because I can't be bothered.
Products
Foot warmer: DO YOUR FEET GET COLD? If so, you may benefit from a foot warmer. I found that, particularly while working from home, my feet would get much colder than the rest of me. Buy today.
Uniqlo clothes: I love the look, I love the price, I love the quality. I will be very sad when one of that trio inevitably slips but so far it's going well! My other favourite clothes brand is Allsaints (for excellent shirts)
Flowers: I love fresh flowers. I find they brighten up a room, provide a nice change, and allow for a little bit of artistry in putting them together. I use Bloom & Wild and get fortnightly delivery.
Window Boxes: Relatedly, I used to live somewhere which was suitable for a window box, and I liked to have fresh flowers every season (without having to buy them myself). So I used Window Fleur to deliver them to me.

Wall Art: I use King and McGaw, the prints have always looked beautiful and been framed nicely. This was my most recent purchase.
Rechargeable Batteries: I hate having to buy and store disposable batteries, it's much easier to just recharge them. I just get Duracell but you can also get the ones that recharge by USB.
Air quality sensor: You should establish whether the air in your house is poisoning you, with small particulate pollution or radon (if you have a basement). A good sensor will tell you this, as well as measuring humidity and CO2 (a useful proxy for whether the air is stale). I use AirThings.
Smart thermostat: You might have a dumb thermostat, which reads the temperature from a single sensor and allows simple time based temperature programming . Further, you probably just set your radiator valves to a generic value that's enough to heat the room. THIS IS BECAUSE YOU ARE A DUMB PERSON. Get a smart thermostat with multiple sensors, which can control radiator valves and program per-room schedules on an app. For advanced mode, some boilers can adjust their output temperature based on commands from the thermostat. I have all my radiators setup with Tado, which also controls my AC units and can turn the boiler off/on.

A powerful dehumidifier: I was initially a bit skeptical of dehumidifiers as I'd only used quite weak ones in the past and they barely made a difference to humidity. I should've known the real problem was how powerful the unit was! I set mine up and it took just a day to fill it's 1.5L tank with water! I have to empty it regularly to keep humidity at around 50% but the house feels a lot less "close" and there is less condensation left around. I use Meaco which conveniently has a slot for an air filter as well.
Cat litter bin: A dedicated bin massively reduces smells from used cat litter and I don't know how we'd live without one. I use Litter Genie.
Automatic cat feeder: If your cat is mostly happy with dry food, why not automate feeding? Saves time, stops you forgetting and means you can leave them for a night without trouble. I use this one but there are many brands.
Heated drying rack: Before I got a dedicated tumble dryer I had a rubbish 2-in-1 washer-dryer. Clothes would not dry properly, and would take ages to dry on the (unheated) rack. An electrically heated rack dried things at least twice as fast. I have this one.
Swiffer mop: I hate regular mops, you have to fill up a bucket, the mop head is always slightly manky, and the process of washing the head while you mop the floor never seems to get things very clean. I much prefer using Swiffer, which has disposable pre-wetted mop heads.
The Ordinary moisturiser: I love The Ordinary, I've been using their skincare for years. Recently switched moisturiser to this one as it was better for my oily skin. I also use their cleanser. My routine is simply: put the cleanser on in the shower, wash it off, apply moisturiser.
Services
Banking: Monzo - I use open banking to bring my other accounts there as well.
Investments: I mostly use Vanguard. They're cheap, have a good selection of the funds I want, and their website is up to date and easy to use.
Gas/Electricity: They all seem pretty similar, but Ovo and Octopus have always done right by me.
House moving services: I don't plan to move house again any time soon, but if I did I would definitely use a moving company to help me do it. If you're London based, I recommend DBM Express (which I was recommended by others on Twitter). They were extremely efficient and minimised stress on a stressful day.
Travel agents: This makes me sound like a boomer but I LOVE using travel agents. I don't enjoy organising holidays (nor does my husband), my preferences are not so niche that they can't be communicated to an agent and I'm happy to pay a little for someone else to handle the aggro. We often take walking holidays, and I've had good experiences with Macs Adventures and Inntravel. For our trip to California, I used the American Road Trip Company.
Cleaner: Just get a cleaner, I don't care if you don't think you need one, get one. This goes triple for people in relationships - you will love your partner 5% more if you don't have to argue about whether the bathroom is dirty enough to clean yet. I used cleaning services for a while, but the best thing is to find a person that your neighbours use and recommend.
Cat sitting: I have had success with CatInAFlat but of course word of mouth/recommendations from neighbours is best.