Hi,
Welcome to the forum.
Zyxel modem/routers are indeed very well respected by the patrons here, I have 2 old Billion models in operation on my son's and daughter's VDSL lines also which perform without any issues, that's the 8800NLr1 and 8800NLr2 respectively, both old models now and probably difficult to source, the r1 version being the better respected model.
I changed these out from the ISP's supplied units in order to run the DSLStats utility and keep an eye on their lines performances remotely.
I picked up a Zyxel VMG3925-B10B modem/router a few weeks ago on e-bay for £30 + P&P, advertised as brand new and unbranded, this indeed turned out to be the case, very pleased with the purchase, currently in use on my line in router only mode.
There are quite a few of this model still on e-bay at good prices, just make sure that they are not locked to an ISP as it takes a bit of tech. knowledge to unlock the units, in worst cases requiring case opening and establishing a serial connection, this would likely be beyond your cumfort zone.
The VMG3925-B10B was supplied by a number of UK and Irish ISP's so there are quite a lot still around some indeed brand new as many customers opted to retain their own devices when changing ISP's but obviously took the offers of free supplied kit at sign up.
As a bonus, if you should ever get the urge/have the requirement to monitor or record your line stat's the Broadcom chipset used by Zyxel permits access via various means with readily available utilities as indeed do the Billion modem/routers mentioned.
Not sure if this facility is available on your current TP-Link modem/router, ie. uses a Broadcom chipset.