I've found myself in a similar situation. What I've learnt is that good load-balancing makes a surprising difference. It won't help you back up your files to the cloud any faster, but it will keep your Internet connection usable for other people while you do so. I've gone from being unable to hold one decent Skype conversation to being able to hold two in parallel on the same network. I've gone from ping times of up to 800ms when my wife used WhatsApp to ping times below 25ms in all realistic load conditions, including WhatsApp, and even flat-out file transfers in both directions at once. For video conferencing and general Web browsing, low latency is usually more important than high bandwidth.

The route I took was to place a small, low-power Linux box between my network and my ADSL router, running OpenWRT, and then configure load-balancing on that. A Web search for "bufferbloat cake" (no, really :-)) will show you one of the most useful Web sites I found.

One other measure you can take is aggressive content-blocking. I use Pi-Hole, uBlock Origin, Privacy Badger and Blokada, and I recommend them all. If you don't have much bandwidth, you don't want to give half of it away to marketers and creepy trackers. Use what little you have to work for you, rather than against you.

Having started from a position of knowing very little about Linux networking, I'd say that the Linux networking stack is powerful, flexible and fast, but it's let down by the available documentation, most of which seems to have been written at least fifteen years ago, and much of which is simply out-of-date. I couldn't find anything that just starts at the beginning and tells you everything you want to know, and is based on modern Linux commands and facilities. I'd write it myself if I understood it well enough but, honestly, I still don't. For anyone who wants to contribute to Linux but is a wordsmith rather than a coder, here's your chance.

I'm sorry -- slip of the keyboard. Where I wrote "load-balancing" here yesterday (not once but twice), I should have written "traffic-shaping." I have only one Internet connection -- that's all I can get here -- but traffic-shaping moves the queue from the ADSL router or the ISP into the little Linux box, where it can be managed better, and ensures that heavy users such as big uploads and downloads don't crowd out interactive users. The Web search I suggested will make more sense in that context!

The home networking space has really been broken for quite a while now. We've forced home users into separate-but-unequal internet using NAT's and forced private addressing. Part of it is there are no more IPv4 addresses to go around anymore. Part of it is that IPv6 has been delayed by 20 years, and now IPv6 isn't what we need at all, frankly.

It seems like lately it's like regular expressions, obscure to many but when you really need it, you really need to know it.

Yeah, and I think it's important to note that there's NOT much incentive for big companies to help us get this right; there's just so much opportunity for them to insert their own little whatever in the middle; so they'll happily partly solve the problem for us, but usually involving phoning home in a way that we don't need.

What's the router that you ended up buying (I'm also giving on load balancing on my own)?

The TP-Link TL-R605. It says a bunch about "Omada" and I still don't really get what that is. Don't worry.

And yes, Amazon et al DO NOT HELP because all of the little boxes look exactly the same, and Amazon will happily recommend the wrong thing. This was how I learned that you can return things at Whole Foods easy.

Just grab something like pfSense or any variant that will give you a GUI to do this wayyyyy more easily and with someone knowledgable configuring it and testing it.

You are waaaay overselling pfSense :) Seriously, I tried it, and sure it's easier than hacking at iptables. But not much.

pfSense gives you the shape of the problem and creates bounds. Being on your own in a text editor with google allows you to shoot yourself in the foot while stumbling in the dark.

Fair comparison, but still a really low bar. It's safer, but not really any easier.