I do not know of any high quality vinyl sofas. Since you can afford it, I would go either with another leather sofa or with a cloth sofa with covers that can be washed, with perhaps a spare cover set kept in reserve. I think leather ages better than vinyl.
IKEA probably offers the biggest selection of cloth sofas with removable covers that can be washed. In Pattaya, I would check Index, of course, but also Boonthavorn Lifestyle furniture on the second floor. Both Index and Lifestyle have some good sales now and then. I think Chic Republic has been selling furniture by Ashley, as well as some other brands.
At the front of the Home Pro on Sukhumvit there is a Jas furniture store as you enter the store. They have a fairly good selection of sofas, mostly recliners, both manual and electric, with some different covering materials available and a wide assortment of colors--including vinyl and leather in different grades. Jas also may be a good option to check as you can customize your choice somewhat. My spouse and I almost bought a sofa from them before we found a bargain at Lifestyle in Bangkok.
If you can get to Bangkok, the Boonthavorn store up the street from Rama 9 mall has a big complex of 3 or 4 stores and the furniture store there is large and on 3 floors with a bigger selection than Pattaya. There's no substitute for actually sitting on a chair or sofa to check comfort. I would never buy anything without first trying it out, so you can check the back height and pitch, the seat depth, and the comfort level of the cushions. Good luck with your search.