Endurance Road Bike for around the £1000 Mark.

My tuppence worth.

Any bike can be an endurance bike, regardless of the marketing schmooze attached to it.

Ultimately, buy a bike that is the correct size for you with enough clearance for wider, comfier tyres and you're almost there. We all change the contact points to reach our desired needs after purchase, so pedals, stems, saddles, tyres etc can be tried and tested ad finitum once you have made your purchase, it's all part of the fun of bike ownership.

As an example, I bought a Focus Mares cyclocross bike just as the pandemic started, a very focused race machine, but by fitting Continental GP5000 tyres and a longer, flipped Easton stem and a saddle that suited my sit bones I now have a comfortable, fast, mile muncher. I regularly ride 100km+, does that make it an endurance bike?

Your biggest problem will be that there is little stock in the £1000 price category, it's the sweet spot for a lot of new riders this summer, so trying to find the perfect bike will be far harder.

Tl;dr don't get caught up too much on the research process, buying a bike and getting out riding should be the priority, as summer is almost over!

Btw I'm 6'4" and a hell of a lot heavier than you and absolutely love my purchase even though it wasn't exactly what I was looking for initially.

At 15.5 stone I'd look at a gravel bike rather than a road bike.  reasoning is that the frame and wheels should be stonger (so resist twisting etc with your mass working on them), also comfort is a priority for you and gravel bikes some with wider tyres which are more comfortable and again protect the wheels from potholes with the large weight on them.  Also they have lower gears which is damn handy if you live in an area with steep hills.  OK it'll be a kilo or more than a road bike.  But I'd rather carry an extra kilo of weight on the than have a mechanical due to pushing the limits fo components.

I picked up a 2017 (little used ) cannondale synapse full carbon ultegra with discs for £1k on Gumtree. I have continued to look on gtree and ebay, if u r not in a rush u can pick up a very decent bike for that sort of money. I think it was tredz that did a write up on the various endurance bikes out there, they are all pretty good, the conclusion being that personal choice would prevail. Try some out whilst saving searches on ebay and gtree.

You could try perusing the buyer's guides, from the menu bar at the top of the page?

Make sure you do a ride test,you said you were looking for comfort and every bike is different. I really wanted an endurance bike . I tested the Giant Defy, Contend and Cannondale synapse. All felt very different. Tried a Trek Domane which I liked, but are expensive for what you get on the cheaper models. Stumbled on the Divege in a sale and took it for a ride.i was not looking for a gravel bike however it was comfy and great spech like the Allez, both are Specialized.

A Specialized Allez would be an excellent choice. 105 groupset, nice Praxis cranks, good wheels (I broke 1 spoke from new, fixed by shop under warranty, all good since).

The stock brakes are fine, but if you want to use it confidently in all conditions you could upgrade to Swissstop BXP pads. I've ridden through some atrocious conditions on my Allez and the braking is consistently good.

Just be wary if you want to fit full length mudguards, I had to do a bit of dremelling as clearance was a bit tight.

i looked for a very long time for an endurance bike for comfort and end up with a comfortable gravel bike with endurance geometry (Diverage E5 Comp 2019)  which was in a sell at £1300.There may be some Diverges still about . Love mine so much.Done Sportives and taken it on fire roads.An do it all bike if you 

The other bike i considered wasthe Giant Contend which is around the £1000 mark.