Yah your predicament is not uncommon.
To use the default database functionality in InfoPath, to query and submit you have to design the form from scratch around the data connection. There still are limitations , such as only one table structure can be used, that may or may not be a problem down the road.
So one option is to start from the beginning and configure this and then replicate your existing form in this new form.
I had recommended the Database Accelerator before since with Web Services you are not bound by the default database rules and have the freedom to have multiple queries and submits along with some other advantages. It is additional middleware, but the tools provided, make developing enterprise solutions much faster and easier.
With DBXL you could convert your existing form over pretty easy.
You can create your own webservices or write code to possibly do some things. You may want to pay for some support help to get you past this hurdle and gain some knowledge.
It is extra hard when you inherit a form rather than architecting it from the beginning.