Based on your description, I would use a standard (SDI) form with a SpliContainer that has buttons in the left panel, and a TabControl in the right panel.
The Buttons trigger TabPage changes, all controls are ready to go and state saved between swaps. An MDI solution will not work, because an MDI form shouldn't contain controls (you could force it, but bad idea), like the left side buttons you want.
It is possible to hide the tabs, so that it doesn't look like a TabControl.
I suggest you take another stab at it. Whatever problems you have, post them and get help.
EDIT:
OP's comment, with better formatting:
Also, to bind a Form to my TabPage
, I had to use this small piece of code
ItemFrm itemfrm = new ItemFrm();
itemfrm.TopLevel = false;
itemfrm.Visible = true;
itemfrm.FormBorderStyle = FormBorderStyle.None;
tabControl1.TabPages[0].Controls.Add(itemfrm);