Are you working? Does your employer have a cycle to work scheme? You might be able to get financial assistance for the purchase of a bike through payroll and save money in tax as well.
As for purchasing a bike, I can’t give any real recommendations, however, I am mega envious of people who have a “bike with a battery”. I often see pensioners overtaking fellow cyclists and also see them flying up hills on them too. If I can find one at a reasonable price I certainly will be looking at getting one to take out the “leg work” of cycling. What is important is getting the fit right. A reputable bike shop will be able to size the bike for you, I wouldn’t recommend “Halfrauds” as they seem to be in the business of volume sales and seem to not train their staff to well. (My opinion hey, each to their own)
As for exercises, I can only recommend weightless squats to start with. I was having major mobility issues recently and a friend recommended squats to kick start my muscles. I did start by using a 12kg kettlebell but it was too heavy and caused me back problems. So it was back to basics and after a few weeks of not using weights my muscles started to build and free up.
Another exercise I do is stand next to your kitchen table and hold the top with both your hands. Then slowly bend your knees (while holding the table) and lower your body down gently down and back up. Do this 10 times to start and after a couple of weeks try to do it 2 to 3 times a day.
Oh, I also am a user of CBD oil now so perhaps that is having a positive impact on my leg cramps as well as my mental health.
All the best