@Francesmalin Sorry to hear your GTT came back suggesting pre-diabetes. Did someone get in touch with you to explain what to do next? Hope you're managing it ok?
To be honest with the clothing question, it really depends a bit. Firstly, on how warm you keep your house overnight and during the day, and secondly on number of layers you're using.
During the day layers are a lot easier, as you can add/take off as you go in/out places. Overnight you want to try to cause as least disturbance as possible really, so getting the layering right can help. I've put a diagram before I used to refer to a lot. You can get sleepsuits that are thicker and have a 2.5 tog rating from Tu like this: https://tuclothing.sainsburys.co.uk/product/tuc144413904?istCompanyId=07cf3c1d-7207-477f-aab0-212732e114dd&istFeedId=03391e81-6312-4095-9322-96087f0115ae&istItemId=mmqwlippq&istBid=t&cmpid=cpc&src=Google&med=Shopping&utm_source=Google&utmmedium=cpc&utmcampaign=21429344369&utmterm=tuc144413904&utmcontent=shopping&utmcustom1=169800185891&utmcustom2=825-875-8916&gadsource=1&gclid=CjwKCAjw8rW2BhAgEiwAoRO5rNKe5B9IByfkH9qRMOSaZqM5lzu4zlJLK8qiII6XyS2qE57rASKewhoCMcEQAvDBwE&gclsrc=aw.ds
Which can be good if your house/room is on the chilly side, as it gives more warmth on the arms. But if you would need to adjust blanket / sleepsack to make sure you don't overheat baby.
You can also buy 3.5 tog sleepsacks (with arms, some of which detach), which is what we use in winter as we live in an old house and it can get quite cold overnight. We have also used more fleecy sleepsuits in the past as well, but the vast majority of our sleepsuits are just cotton.
The main things in terms of safety, are just to check baby is a good temp when they wake up (they'll be waking up so regularly the first 3 months 2 years 😂) you'll have plenty opportunities to check temp is ok. Also, never put a hat on when asleep (it can slip down and cause a suffocation risk), use 'cellular' blankets if you're using blankets (i.e. ones with holes in them, as it means if baby was to cover face they are less likely to suffocate), never use a hot water bottle etc. If you're co-sleeping, baby shouldn't be under your blanket/duvet. So when my DD was little, she was in her sleepsack with nothing around her, and I used the C curl position with my duvet tucked under my body and lower down than I would normally have duvet. I know some people prefer to use a single duvet when cosleeping.
In the car, baby should not be in a jacket / pram suit. If the car is cold, use a blanket over them, so you can remove it easily when car warms up. Second safety part to this is also baby wearing a jacket / pram suit etc actually stops their seatbelt/harness from being tight enough, which is also why the blanket should be on the outside of the harness. Also, just be cautious about using a pram suit if you have a miracle child (unlike my first!) who stays asleep in the pram when you come home / go inside anywhere and stop moving. Baby could easily overheat in a pram suit inside, so if your baby is a good sleeper in the pram, you might want to use blankets instead as these can be removed / added. Also be aware the same is true when using a carrier/sling, if baby comes inside and is still in the sling (which counts as a layer) and its warm inside, then you need to consider your layering approach (e.g. less layers on baby, and more around baby, like a fleecy cover for your carrier, a coat that you wear the sling underneath etc).