No need to be scared, although I agree it can be very confusing with all the different companies and offers.
Firstly, do you actually want extras like apps, a subscription/membership, online coaching (sometimes that's AI based) etc? If you don't you can just eliminate those companies from your short list.
There is a price comparison site called https://monj.co.uk which lists the prices for each dose, either with a new customer discount applied, or you can change it to show you the prices without the new customer discount. The table also has a column on the far right that shows if that pharmacy is a subscription based service and whether it offers additional support/extras. You obviously only get the new customer discount for your first order, but you can change pharmacies each month if you want or need to, to take advantage of their new customer discounts.
Everyone starts on the 2.5mg dose for Mounjaro, so that's the price you'd be looking at initially. All the pharmacies listed on Monj are GPhC registered and regulated, and the medication they supply is the same. So I'd be mostly guided by price, and by the TrustPilot score/reviews as well.
In terms of loose skin, it's down to age, genetics and previous skin damage more than anything else. Speed of weight loss might make it seem worse initially, if you get any loose skin, but it does get better with time. I lost a lot of weight in the early days, and I started off with a massive double chin, but I have not got a terrible saggy neck now. I was one of the people who found the effects started from day 1, whereas many people find it takes a few weeks to get going, so although fast weight loss is what hits the social media headlines, it isn't to be expected or even typical.