I have a new oil combi boiler....water has a megaflo, and we use the thermostat to control the heat. Tups
Not sure you meant that you have a combi boiler (some confuse combi with condensing, hence the move to calling them 'high efficiency'), not mutually exclusive to have a combi and a hot water cylinder, just not commonplace....but that's not relevant to your request for advice.
Here's mine:
I have fitted Nest, Lyric, and Honeywell Evohome.
The Nest is a lovely piece of kit, its packaging reminds me of iPhone, and that's not surprising as it was designed by a former Apple employee. In use the thermostat feels high grade, and the schedule settings (yes, you WILL start to use them once you see the benefits) are almost intuitive. It does have its faults though, the remote relay unit (containing the relays to control heating and hot water) is a pain to install because the terminals are too small, i.e. too small to get two 0.5mm2 solid conductors in together (required if switching mains to a zone valve) and, if using stranded cables the IEE regs require ferrules to be crimped over the strands and the same problem remains. It also requires an internet connection, which many old people will not have.
The 3rd generation one has the hot water function, and costs about £200, but if you just want the heating function then earlier ones may be available on EBAY, Gumtree, et al at reduced prices.
The Evohome is great, and can do everything the others do and more, but is very expensive, and needs a little (just a little) more tech knowledge to get it up and running. It is far more expandable, but in my opinion if you're going to fork out about £400 for a typical system you'd want something more futureproof...IMO the Evohome has a few design edits to come i.e. compatability with a "common" interface to allow other manufacturer's kit to integrate with it would be very useful. The std display is good, but if using anything but the table mounted stand (supplied) you'll be asked for another £50 for the wallmount. The additional roomstat sets rely on batteries for their comms (a pet hate of mine), and don't have the smooth feel of the Nest, nor are they big enough to cover a std 76mm x 76mm box, previously used to mount the old mechanical thermostat (the Nest comes with a white plastic facia plate to solve this)
The Lyric is a std thermostat replacement, costs about £110, and does basic control. It has a large temperature display, and schedules if you want them. I believe there are hard wired and wireless versions, I've only fitted the hard wired version because of my irrational fear of batteries!
Again, an internet connection is required for remote operation, and in common with just about all connected control systems, an Android phone or Apple iPhone as no one seems to write apps for Windows based phones.
Some years ago, in the days before smarty-pants phones, I envisaged a modified central heating programmer which had a slot for a SIM card, the idea being I could send one of four text messages directly to it from my Nokia 3320, namely CH ON, CH OFF, HW ON, and HW OFF. I approached several controls manufacturers, none of whom showed much interest. Clearly that method of operation would suit your needs, and that of many families of non-connected old people, but it never caught on, and probably will never do so.
Hope this longer than anticipated reply helps.
MM