Hi Trina,
For shoes boots [ specifically large ladies sizes, Try Chiltern Street. nearest tube station is Baker street
There are number of specialist shoe shops there. I like Crispinshoes
http://www.crispinsshoes.com/
As for being shy , take a deep breath, smile and enjoy , and above all try on every potential purchase.
if it does not feel right -dont weaken.
Part of shopping is knowing that you have exhausted all the possibilities !
An essential part of which is getting a dead comfortable pair of shoes to walk the walk.
As for Hose , anywhere really I would try the big department stores on Oxford Street , Price will be okay and they have a large range.
Finally , London is big and so can be very anonymous ,no-one will notice you , just go out and enjoy getting something you will enjoy walking in and wearing . Hope it goes well Donna