i was wondering when the best time is to move from a cot to a toddler bed (floor bed) and also use a pillow (she has a nap on the lounge with a pillow during the day and seems to love it. My 15 month old is not sleeping through the night and wont go back to sleep unless being held or holding her hand. i have tried to put her in my bed on occasion using the co sleeping safe sleep guides yet she wont sleep in our bed as the mattress is uncomfortable for her.

There is no specific age when moving a child from a cot to a bed is recommended.
However, there are a number of safety issues that need to be considered when a child is no longer in a cot.
This includes things around the house that a child would have access to once they are out of a cot eg stairs, power points, windows, doors, furniture etc - see information linked for further examples.
Have a look at our cot to bed information.
https://rednose.org.au/downloads/RN0407_22_Cot-to-Bed.pdf
https://rednose.org.au/article/making-your-home-safe-before-moving-a-child-from-a-cot-to-a-bed
https://rednose.org.au/article/where-to-sleep-a-child-who-has-moved-from-a-cot

The general recommendation for moving to a bed from a cot is:
“For safety reasons, when a young child is observed attempting to climb out of a cot and looking like they might succeed, it is time to move them out of the cot. This usually occurs when your toddler is between two and three and a half years of age but could be as early as 18 months.”
https://rednose.org.au/downloads/RN0407_22_Cot-to-Bed.pdf
There are many reasons why children’s sleep patterns change - maybe it would be worth having a chat to your local Maternal/Child Health Nurse or contacting a local support service who can discuss settling tips for your daughter.
Let me know what State you are from & I can give you some local contact details.

Pillow use is not generally recommended for babies who are sleeping in a cot & are less than 2 years of age.
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows
https://rednose.org.au/article/can-baby-use-a-pillow-to-prevent-flat-head