Thanks for your patience.
I’m afraid that the solicitors that you have spoken to are correct: if you submit an application from within the UK then it will certainly be rejected. This means that you would either have to leave the country or appeal. Your chances on appeal would not be great and if - as is possibility - it is rejected then you would have to leave the UK and apply from your home country any way.
So, the best way forward would be for you to instruct a solicitor in the UK to prepare your application and supporting evidence now so that you can take it to your home country and submit it as soon as possible. Having an application drafted by a solicitor will guarantee the the home office case worker will be able to approve it quicker than they would do if you had prepared it yourself.
I know it’s frustrating, but you have overstayed your visa and the choice that you now face is a result of that. Unfortunately, there have to be consequence when a person breaches the immigration rules and requiring you to return home in order to make your application is one such consequence.
The most efficient, quickest and cheapest way of securing your leave to remain if to submit your application from your home country after it has been prepared by a solicitor in the UK.
My goal is to provide you with a good service. If you feel you have received anything less, please reply back as I am happy to address follow-up issues specifically relating to your question.