Thanks a lot for all the feedback, it is very useful. I was in another bike shop today and now have other options on the table, but one major point i failed to mention in my opening post is the reason i have decided to give road cycling a go in the first place.
In 2019 i had surgery to remove a herniated disc from my lumbar spine, at L5>S1 level. I have had ongoing problems since. I am slightly overweight, with a bit of a belly. Over the last year or so i have been looking at ways to loose some weight and strenghten my core, without aggrivating my lumbar spine problems. Swimming was going well until i got bursitis in my shoulder which is ongoing for 6 months now. I noticed cyclists all tend to be in great shape, usually they are pretty thin with strong looking cores. I also like the idea of getting outdoors more.
I was talking to a cycling friend the other day. Possibly the aggressive riding position of a road bike could do me more harm than good, so perhaps i need to consider another bike style? I have an MTB for 18 years, but have not ridden on it for around 10 years, its a bit of a slog getting around on it, possibly due to the wide square grilly type of tyres it has, i never really liked riding it much. For me to take to cycling regularly, and go out on long cycles for 1>3 hours, i need a bike that glides comfortably across the road, and i think a road bike seems ideal, other than the aggressive riding position. I'm not familiar with bike styles, road/gravel/endurance etc. Probably it is best for me not to buy a bike just yet and to loan out a bike for a day or two and see how my back takes to it, and to see which style of bike i get on best with. I have heard
Decathlon loan out bikes, but i'm not sure which models etc they have on offer for loaning. I'll look i to it, and in the meantime i'll try to hold back on making any impulse buys like on the special deal they gave me for the Cannondale.