Regarding the cheaper Samsung model, I looked at detailed info on the AV Forum and it shows the TV is "HD Ready" (vs Full HD).
(I had initially included that set, because of the price, and then when I searched a bit longer, saw it was not 1920 x 1080. Once I found that info, I went looking again!)
"HD Ready" means it is still in the right widescreen proportions (16:9) [ vs the older style TVs with 4:3 width:height ] but with 1366 x 768 there are fewer pixels on the TV, so the screen has about half the pixels on it, and picture quality is reduced.
It will show the picture and fill the screen OK, but as you have Sky HD, it would be worth paying more so when you select an HD channel you should get a better picture from the Full HD TV, and LCD TVs are giving good pictures (where 2+ years ago, plasma sets were significantly better, but costing up to 1500 pounds).
As for size... well, I would think a 32" should still be considered. I have a 28" widescreen TV that is perhaps 5 or 7 years old, very deep and quite heavy. When I replace that TV, I will be able to have a screen at least 1.5 feet further away (I generally view from about 8' to 9' away), and would be looking to get 37" or 42", sitting it on a stand about 6" above the carpet if necessary!!
It will depend to some extent on where you will put the TV. Clearly many older TV stands put the bottom of the TV screen around 18" from the floor.
As you will probably want the vertical mid-point of the TV screen to be roughly the same height as now (so you are not needing to bend your neck awkwardly to look up or down when viewing the screen), the stand would probably need to be a bit lower.
I'd say your best bet is to get a tape measure and note the distance from the carpet to the bottom of the visible picture and also the distance from the carpet to the centre of the screen.
Then visit Asda Living / Comet / Currys / Tesco - whichever is most convenient, and check the height of the screen. You can then see how much larger it is vertically than your existing TV and judge the new (lower) stand you would need. Also, you can work out how much higher the top of the TV will be compared with now. I have not sat down to calculate the sizes, but obviously the width increases more than the height.
Also, depending on the height of the TV, would it be visible outside your home - walking past a house near me, the TV screen is massive (50" or larger), and, along with 4 tall speakers, it could be "begging" to be stolen as there is no way to hide it, and the family cannot even see around it (to spot me noting how many cables they have :) )