The most common and most likely answer to this crossword clue is the 5 plus 8 letter word LOTUS POSITION
I've seen this crossword clue in Financial Times
L
O
T
U
S
P
O
S
I
T
I
O
N
More clues leading to the result LOTUS POSITION
Buddy explains!
The straight part
We know that "Sitting cross-legged in this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sitting cross-legged in this = lotus position.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.