I find the request for "thick" to be quite confusing as this is a descritpor for consistency. Does afviper want something that one needs to spoon out of a bottle?
Perhaps á la Heinz Ketchup?
If the request is merely for rich, full-bodied and full-flavoured. then I would agree with many of the suggestions above.
My own list of offerings would probably lean more towards the sherried style and include:
Macallan 18y "Sherry Oak", dated versions with "Classic" labels
Glenrothes but only older offerings - 19 years old or more
Glenfarclas Quarter Cask
Definitely Glen Garioch 15y and older
The various Bruichladdich 20 y/o 1986 "Sherry" bottlings would also fit the bill
Another and maybe a surprise addition to my list would be Auchentoshan 3 Wood. This is a Lowlander, but it joins my list thanks to the effect that all that wood has had on it during maturation.
But possibly the thickest and richest of all would be the newly released Dalmore 40 y/o ...... but for a price of around 50 USD? ..........
If I look at the world of peat, then I may suggest:
Ardbeg & Laphroaig as others have done, but possibly the "richest" or "thickest" would be Bruichladdich PC5.
Just my opinion,