There's a plethora of products to choose from, and my previous blog post has details on how to choose yourself. BUT if you just want someone to choose for you, I'll post links and comments below to make your choice quicker.
Cheap & Cheerful: if you're a beginner it'll do the job but you'll find it frustrating and quite hard to hold poses due to slipping. But if money is tight, either choose something cheap on eBay or Amazon, or buy this:
cheap and effective, but DOES SLIP so But if you have no trouble holding down dog then it's a cheap solution. I did 2 weeks of twice-daily yoga training on one of these and by the end didn't notice the slipperiness, as I had adequate muscle memory, so it can work. Also Yogamatters is a black woman owned business (if you are keen to support #blacklivesmatter ; Yogamatters also sell other great products, too.)
Non-Slip Mats (Rubber / TPE) - more expensive but less frustrating from a slipping point of view; I have paid for all 3 of these mats which i will link, but you might want to make your own selection of length (there are slightly longer mats for taller people, for an extra £5 or so) etc.
Jade - Harmony 5mm mat: £70 my husband's favourite; the GRIPPIEST natural rubber; he likes it also cause it is more breathable than the other mats;
Liforme 5mm mat - £100, currently on sale for £90; my personal favourite, but also the most expensive; grippy enough but not as grippy as Jade (or the reversible back of lululemon (which for me is better as I can slide my foot a little here or there, eg. slide to a wider stance)
Lululemon 5mm mat - £58. Reversible: one SUPER grippy side AND one Normal Grippy side. Currently surprisingly the best value for money in my opinion if you want to buy just 1 mat. (Surprising only as they are a premium yoga brand). Comfortable cushioning, 2 great grip options, used in many studios worldwide. I personally have the 3mm one and I just don't find it thick enough without another mat underneath it; in my local studio I use these 5mm ones.
General guide:
1. If you're only going to buy 1 mat, get a minimum 4mm mat for comfort. Anything lighter will make kneeling etc. uncomfortable, even if you daydream about how much easier it will be to travel with a light mat. (First mat I bought was 3mm, I thought it would be a good compromise for light weight and comfort, but once I had a 5mm I literally never used it again, I just find it too uncomfortable.)
2. Any cheap mat will do, BUT especially if you're a beginner, you'll find it's slipperiness very frustrating. Downward dog is much harder when your hands are sliding away, and you'll use it as an excuse to say yoga isn't for you.
My recommendation: IF you're going give yoga a proper try, it is worth spending £60 on it. BUT if you aren't sure, buy the cheapest mat you find, and then try my mat in comparison to it. Then you can still buy the travel (1.5-3mm) version of my super nice mat for less, and just place it on top. You'll still end up spending at least £50+, and carrying two mats around, but on the plus side you'll have a travel mat, extra cushioning, and not a big upfront investment.
For more detailed options and opinions look at my previous blog post on Yoga Equipment.
Hope this helps and I would LOVE to hear your thoughts, comments, experience, and questions in the comments below!