You cannot do these things no, you will need to buy a new device of some kind. The easiest fix is to buy a legacy Openreach modem e.g. a HG612, it will work, but it's lacking some of the newer standards. This will act as your modem, so plug the router into here.
(Assuming BT). Setup the router to connect with the following details. Not sure if your Merlin device supports this, but I am sure it will.
Username:
[email protected]
Password: BT
VLAN: 101
VPI: 1
VCI: 32
Yes your experience of VM is very lucky indeed, we are not this fortunate in London (tried it in 3 properties now). Pings are like 35+, plenty of areas "high utilization which is service affecting" with the fix dates being pushed back over 2 years. 360P streaming on an evening, YouTube struggling with 144P on Sunday evenings. Granted, they let me leave, twice.
Once you are up and running I confident you will be happy, albeit at slighty lower speeds, but in all honesty I do 4K streaming, netflix, Sky Q 4K downloads, we have iPads, laptops, chromecasts, fire TV Sticks, 2 Sky Q HD boxes on the WiFi, smart tvs, ps4s, xbox, Wii, basically all the tech and it works wonderfully. I have 38Mbps and I do not feel the need for anything faster right now, we can do more than 1 4K stream at once.