Private Health Insurance

I make no claim to be 100% accurate but common sense says there are things to consider.
Is your attorney Belgium based and thus familiar with the legal implications of what is suggested? If not, why are you considering that they might be right?
If your attorney IS Belgium based are they prepared to put their recommendation in writing so that you have some defence when you find that the advice is wrong?
Health insurance is commonly provided by a mutuelle and everyone living here has to be covered. I would expect anyone providing private health insurance to ask why you are not so covered. And, as such, you may not be able to find cover.
And, for example, if you imply that you are a visitor rather than a resident, you may find that any claim you make will be refused if the truth comes to light. And they will not refund any premiums which you have paid.

I'm assuming that you live in Belgium; in that case contact a mutuelle (Parténamut for instance who have a special expat program - https://www.partenamut.be/fr/partena-expats) and ask them.

This shows that they have a "cross-border worker" category in their expat services:
"A VIP service for expats and companies
We assist you in the formalities required to register for social security (healthover) and simplify your settling down in Belgium. Whetever you are a diplomat, an employee, a self-employed, on a temporary posting, a cross-border worker or any other activity, we advise you free of charge. Just contact us!"