Hi Sue,
I think Dave's advice is good, there is a good chance that you will end up with an exercise bike that is unused and gets in the way somewhere in your house. It can work though, I have one and I can pedal for ages on it but I have spent a lot of my life out mountain biking. If you do get one then you need something to distract whilst pedalling like listening to music or watching tv or ideally a route simulation (some good bikes will have a screen that shows you doing the Tour de France 😁), otherwise it's too easy to give up. Also, it is advisable to vary the resistance e.g. do 5 mins easy, then 5 mins hard as if going up hill, then back to 5 mins easy again etc. If you can get a routine going then it is good exercise and a sure way to lose weight. A few years ago prior to my PCA, I used to nip into a gym before work for 4 days per week and I managed to do 40 minutes each time. I never, felt so good and I lost weight. However, I am struggling now though as I am on HT, of which the impact of it on my body, makes any exercise difficult.
As Dave advised, try find a 2nd hand bike to start with or maybe go try for a trial at a gym?
all the best
Spongebob