I'll start by asking the usual, "where are you". If you fill in your location this helps others help you.

Then it depends if you really want all that chassis stiffness, ie high performance, track work etc (a cage and a few strut braces may do the job).

But if you want it done, you can do it yourself. Weld about 20-30mm long, then leave about twice that or more space between the next weld (to allow for chassis flex, otherwise it'll crack).

Make sure not to weld forward of the front strut towers or rear of the rear strut towers.

If welding thin sheet metal is not your idea of fun, there's plenty of places that should be able to help. I can give you a few places in Melbourne that do good work.