"睇起身" does not exist in Cantonese.
"That looks great! " can be translated as below.
1. 嗰個 睇嚟 好似好正！[ 嚟=lai, pronounced with the 4th tone ] ( not quite sure )
2. 嗰個 睇嚟 好正！( not 100% sure but quite sure )
嗰個 -》 That
睇嚟好似 -》 looks
好正 -》 great
睇嚟 - it looks
好似 - it should be
It's very common to bind them together "睇嚟好似", meaning that you are not quite sure, but it looks great.
However, It is not appropriate to use "正呀" because the wording is too strong. It implies you are 100% sure that is perfect, not just "looks great".
嗰個正呀! ( when someone get excited on something :) )
We usually do not use "正" to address people in the second person form ( "you" form) as it is too strong in feeling, especially with people you are not familiar with. More often, we use the soft word "好“ or other precise wording instead.
It is OK to use it to address the third person( person A & B talking about C, but it is informal situation )
It is a culture different
In English, we can say, "Good morning, you looks great!"
In Cantonese, we simply say "早晨！( good morning )”
If you really want to translate "you looks great!", here are the replacement word.
1. 好精神 (full of energy, for elder people )
2. 好靚 ( pretty, for girls )
3. 好型 ( handsome, for boys )
4. ....many other words for different situations