usually Penang asks bank statement showing only 200,000 or more baht, that doesn't need to be on account since 2 or 3 months: just few days before visa application are enough.
Can check with my agent in Penang if affidavit letter WITHOUT bank statements is fine.
Usually they ask only statement or both letter and statement
yes, you can apply for a Single Entry Tourist Visa at Thai Embassy in Vientiane. When you re-enter Thailand your passport will be stamped by 60 days, before this stamp run out you can extend it by 30 more days at local Immigration
Satun border accepts South Koreans and give 90 day stamp even if back-to-back if they go with an agency and pay an extra fee of 3,000 baht (1,000 per month).
Your easier option is to buy a 30 day extension at local Immigration (1,900 baht).
If you decide to go out/go in, you will get a 30 day visa exempt stamp, both by plane and by land (15 day stamp doesn't exist anymore since 31.12.2016); by the way entries by land are limited at 2 per calendar year; entries by plane are officially unlimited.
You can extend your 30 day stamp too, same procedure and cost of extending a Single Entry Tourist Visa.
You and your husband can apply a single entry Tourist Visa only in a Thai embassy or consulate outside Thailand, then you can get a 60 day stamp on arrival and you can get a 30 day extension at any local Immigration office paying a fee of 1900 baht.