The fog and cobwebs have receded from the deepest reaches of whats left of my mind and reminded me of the TP-Link TL-MR3020.
These things are a mini multi mode travel router. About 6cm square. The have a built in Wireless Bridge mode (among others) and in terms of setup and use they are a living physical example of the ultimate implementation of the KISS principle.
Flip a switch on the side to the appropriate mode, plug it in, boot it up, access setup webpage and tick boxes and it just works.
https://www.tp-link.com/au/home-netw...3020/#overview
The last time I remember having my hands on one (or actually a few of these) of these would be about 10 years ago.
So imagine my surprise to see that TP-Link still makes them and you can still buy them for $35 to $45. Around the same price when I last bought them.
https://www.ebay.com.au/itm/184379149649
If you don't have any success getting the WDS to work on your old router then this will be your quick and cheap answer.
Work colleagues and I used to use these routers with our then brand spanking new Galaxy S2 phones.
The company I worked for had Telstra Business accounts and there must have been something special about them because the phone would run at the max 3G speed all day every day without question, a wonderful 21Mbps back then. The phones would run so hot we'd have to put them in ice packs.
We'd use the 3020 as a 3G to Ethernet bridge so we could plug it straight into our home networks to get speeds far higher than the sh*tty ADSL that was available in our areas.